The Epilepsy Prescriber's Guide to Antiepileptic Drugs

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The Epilepsy Prescriber’s Guide to Antiepileptic Drugs

The Epilepsy Prescriber’s Guide to Antiepileptic Drugs Philip N. Patsalos FRCPath, PhD

Professor of Clinical Pharmacology & Consultant Clinical Pharmacologist UCL Institute of Neurology, The National Hospital for Neurology and Neurosurgery, London, and the National Society for Epilepsy, Chalfont St Peter, UK and

Blaise F. D. Bourgeois MD

Professor of Neurology, Harvard Medical School Director, Division of Epilepsy and Clinical Neurophysiology William G. Lennox Chair in Pediatric Epilepsy Children’s Hospital Boston, USA

CAMBRIDGE UNIVERSITY PRESS

Cambridge, New York, Melbourne, Madrid, Cape Town, Singapore, São Paulo, Delhi, Dubai, Tokyo Cambridge University Press The Edinburgh Building, Cambridge CB2 8RU, UK Published in the United States of America by Cambridge University Press, New York www.cambridge.org Information on this title: www.cambridge.org/9780521687164 © P. N. Patsalos and B. F. D. Bourgeois 2010 This publication is in copyright. Subject to statutory exception and to the provision of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published in print format 2010 ISBN-13

978-0-511-72947-8

eBook (NetLibrary)

ISBN-13

978-0-521-68716-4

Paperback

Cambridge University Press has no responsibility for the persistence or accuracy of urls for external or third-party internet websites referred to in this publication, and does not guarantee that any content on such websites is, or will remain, accurate or appropriate. Every effort has been made in preparing this book to provide accurate and up-to-date information which is in accord with accepted standards and practice at the time of publication. Although case histories are drawn from actual cases, every effort has been made to disguise the identities of the individuals involved. Nevertheless, the authors, editors, and publishers can make no warranties that the information contained herein is totally free from error, not least because clinical standards are constantly changing through research and regulation. The authors, editors, and publishers therefore disclaim all liability for direct or consequential damages resulting from the use of material contained in this book. Readers are strongly advised to pay careful attention to information provided by the manufacturer of any drugs or equipment that they plan to use.

Contents Preface Introduction

page vii ix

1 11 19 31 40 49 59 68 77 86 95 104 111 124 134 145 153 163 173 181 192 204 212 220 230 238 246 255 263 274 288 297

Abbreviations Interaction Table Index

307 308 310



Acetazolamide ACTH Carbamazepine Clobazam Clonazepam Diazepam Eslicarbazepine acetate Ethosuximide Felbamate Fosphenytoin Gabapentin Lacosamide Lamotrigine Levetiracetam Lorazepam Methsuximide Midazolam Oxcarbazepine Paraldehyde Phenobarbital Phenytoin Piracetam Pregabalin Primidone Rufinamide Stiripentol Sulthiame Tiagabine Topiramate Valproate Vigabatrin Zonisamide

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Preface

Preface

With the rapidly increasing number of available antiepileptic drugs to choose from, those involved in any aspect of the treatment of patients with epilepsy face the challenge of remaining familiar with all relevant aspects of every medication that is currently available, including the newest ones. The purpose of The Epilepsy Prescriber’s Guide to Antiepileptic Drugs is to present all the necessary information in a format that allows the prescriber to easily and rapidly find the specific answer to any question that may arise in the process of initiating and monitoring a medication for the treatment of epilepsy. As opposed to standard textbooks, this unique guide focuses, in a systematic and didactic manner, on all the information that the prescriber will need to choose and use a medication, as well as on features of the drug that may need to be discussed with the patient before or during treatment. The topics covered for each drug follow an identical sequence and include chemical name and structure; brand names in major countries; generics available; licensed indications; nonlicensed use; seizure types for which the drug is ineffective or contraindicated; mechanism of action; pharmacokinetic parameters; interaction profile; common, lifethreatening, or dangerous adverse effects; dosing and use; laboratory monitoring; use in special populations (renal and hepatic impairment, children, the elderly, pregnant, and breast-feeding women); the overall place of the drug in the treatment of epilepsy; suggested reading. The reader can use this guide in many different ways and for various purposes, such as to rapidly review a synopsis of all relevant aspects of a given drug, to choose a drug for a patient by reviewing the spectrum of efficacy and adverse effects of several drugs, to find the answer to one specific question about a specific drug, or as a guide to discuss precautions and adverse effects with a patient before or during treatment. In all instances, this information will be rapidly and easily found.

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Introduction

Section 1: Therapeutics Covers the chemical name and structure; brand names in major countries; generics available; licensed indications as approved by the United States Food and Drug Administration (FDA) and the European Medicines Agency (EMA) or the United Kingdom Medicines and Healthcare products Regulatory Agency (MHRA); nonlicensed use; seizure types for which the drug is ineffective or contraindicated; mechanism of action; efficacy profile.

introduction

The purpose of The Epilepsy Prescriber’s Guide to Antiepileptic Drugs (AEDs) is to provide practical and concise information so as to allow the optimum use of AEDs in clinical practice. This quick reference guide provides a wealth of invaluable information for use by all who treat patients with epilepsy, including neurologists, neurosurgeons, general physicians, those caring for the elderly, emergency medicine doctors, medical students and trainees at all levels, general practitioners, nurses and epilepsy nurse specialists, and practice pharmacists. All of the drugs are presented in the same design format and in alphabetical order to facilitate rapid access to information. Specifically, each drug is divided into eight sections and each section is designated by a unique color background: therapeutics, pharmacokinetics, drug interaction profile, adverse effects, dosing and use, special populations, and the overall place of the drug in the treatment of epilepsy, followed by suggested reading of key references.

Section 2: Pharmacokinetics Highlights the pharmacokinetic parameters relevant to each drug’s clinical therapeutics and includes absorption and distribution, metabolism, and elimination parameters. Section 3: Drug interaction profile The interaction profile of each drug is divided into three major sections which include pharmacokinetic interactions, pharmacodynamic interactions, and interaction with hormonal contraception. The pharmacokinetic interaction section is further subdivided into interactions between AEDs and interactions between AEDs and non-AED drugs. Noninteracting drugs have been omitted. Section 4: Adverse effects Explains how the drug causes adverse effects; contains a list of common, life-threatening, or dangerous adverse effects; an effect on weight is noted, and advice about what to do about adverse effects. Section 5: Dosing and use Provides the usual dosing range; available formulations; how to dose and dosing tips; how to withdraw drug; symptoms of overdose and how to

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the epilepsy prescriber’s guide to antiepileptic drugs manage; what tests and therapeutic drug monitoring are needed; other warnings and precautions; and when not to use. Section 6: Special populations Gives information about use of the drugs in the presence of renal and hepatic impairments, and any precautions to be taken for treating children, the elderly, and pregnant and breast-feeding women. Section 7: The overall place of the drug in the treatment of epilepsy This section provides an overview, based on the authors’ opinions, as to where each AED can be placed in relation to the treatment of patients with epilepsy and summarizes the primary and secondary seizure types for which it shows efficacy, and finally highlights the potential advantages and disadvantages of each AED.

introduction

Section 8: Suggested reading In this section, the authors highlight the key references that were used in compiling the information contained in each drug section and readers are advised to read these if more information is needed. Readers are also encouraged to consult standard comprehensive reference books on epilepsy and AED textbooks for more in-depth information. At the back of the guide is an index by drug name. In addition, there is a list of abbreviations and a table highlighting the interactions that can occur between the different AEDs.

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the epilepsy prescriber’s guide to antiepileptic drugs

Acetazolamide Therapeutics Chemical name and structure: Acetazolamide, N-(5-(aminosulfonyl)-1,3,4-thiadiazol-2-yl)-aceta­ mide, is a white to faintly yellowish white odorless crystalline powder with a molecular weight of 222.25. Although a sulfonamide compound, it is unlike sulfonamide antibiotic compounds. It does not contain an arylamine group at the N4-position, which contributes to allergic reactions associated with sulfonamide antibiotics. The structure of acetazolamide bears some similarity to that of zonisamide. Its empirical formula is C4H6N4O3S2. N N O CH3

C

NH

SO2NH2

therapeutics

S

A

Brand names: • Acetadiazol; Acetak; Albox; Apo-Acetazolamide; Azol • Carbinib; Cetamid • Diamox; Diamox Sequals; Diamox Sustets; Diluran; Diural; Diuramid • Evamox • Fonurit • Glaupax • Huma-Zolamide • Ledamox; Lediamox • Medene • Optamide • Renamid • Stazol; Synomax • Uramox • Zolmide Generics available: • Yes Licensed indications for epilepsy: • Adjunctive treatment of generalized tonic–clonic and partial ­seizures (UK-SPC) • Adjunctive treatment of atypical absences, atonic, and tonic ­seizures (UK-SPC) • Intermittent therapy of catamenial seizures (UK-SPC) Licensed indications for non-epilepsy conditions: • Adjunctive treatment of glaucoma (UK-SPC; FDA-PI) • Prevention or amelioration of symptoms associated with acute mountain sickness (FDA-PI)

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Nonlicensed use for epilepsy: • Lennox-Gastaut syndrome Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Acetazolamide is not contraindicated for any seizure type or epilepsy; does not commonly exacerbate seizures

Acetazolamide

Mechanism of action: • Potent inhibitor of brain carbonic anhydrase, the enzyme that reversibly catalyses the hydration of CO2 and the dehydration of carbonic acid • The carbonic anhydrase inhibition results in an elevation of intracellular CO2 , a decrease of intracellular pH and depression of neuronal activity • Acetazolamide increases the concentration of weak acids (such as certain antiepileptic drugs, e.g., phenytoin and phenobarbital) into tissue; this may account for part of the efficacy of acetazolamide as add-on therapy • Tolerance to the effect of acetazolamide often develops, possibly as a consequence of increased carbonic anhydrase production in glial cells Efficacy profile: • The goal of treatment is complete remission of seizures • Onset of action may be rapid and usually within a few days • Tolerance to the effect of acetazolamide often develops within 1–6  months • Discontinuation of treatment may re-establish efficacy, making acetazolamide particularly appropriate for intermittent use, such as in catamenial epilepsy • Acetazolamide is used more commonly as an add-on antiepileptic drug than as monotherapy • If acetazolamide is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: >90% • Food co-ingestion: neither delays the rate of absorption nor reduces the extent of absorption • Tmax: 2–4 hours • Time to steady state: 2 days • Pharmacokinetics: linear

the epilepsy prescriber’s guide to antiepileptic drugs • Protein binding: 90–95% (90% of the drug in the body is bound to tissue carbonic anhydrase) • Volume of distribution: 0.3 L/kg for total concentration, 1.8 L/kg for free concentration • Salivary concentrations: it is not known whether acetazolamide is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

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Metabolism: • Acetazolamide is not metabolized

Drug interaction profile

Elimination: • Half-life values in adults are 10–15 hours • Renal excretion:  100% of an administered dose is excreted unchanged in urine Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on acetazolamide: –– To date, there have been no reports of AEDs affecting the clearance of acetazolamide and affecting acetazolamide plasma levels • Interactions between AEDs: effects by acetazolamide: –– Acetazolamide can increase carbamazepine plasma levels –– Acetazolamide can increase the free fraction of phenytoin –– Acetazolamide can increase the tissue concentration of other AEDs (e.g., phenytoin and phenobarbital) –– Acetazolamide can decrease the absorption of primidone • Interactions between AEDs and non-AED drugs:  effects on acetazolamide: –– To date, there have been no reports of other non-AED drugs affecting the clearance of acetazolamide and affecting acetazolamide plasma levels • Interactions between AEDs and non-AED drugs:  effects by acetazolamide: –– Acetazolamide can increase cyclosporin plasma levels –– Acetazolamide can decrease lithium plasma levels Pharmacodynamic drug interactions: • It has been suggested that the efficacy of acetazolamide in the treatment of seizures may be due in part to a pharmacodynamic interaction with other antiepileptic drugs • Acetazolamide prolongs the effects of amphetamines and quinidine • Anorexia, tachypnea, lethargy, coma, and death have been reported in patients receiving concomitant high-dose aspirin and acetazolamide • Acetazolamide and sodium bicarbonate in combination increase the risk of renal calculus formation

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Hormonal contraception: • Acetazolamide does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects How drug causes adverse effects: • Carbonic anhydrase inhibition by acetazolamide is likely to be the mechanism responsible for the clinical adverse effects, such as metabolic acidosis, paresthesias, and kidney stones

Acetazolamide

Common adverse effects: • Paresthesias, mostly tingling in the fingers and toes • Drowsiness • Ataxia • Blurred vision • Frequent urination • Alteration of taste (parageusia), especially for carbonated beverages • Metabolic acidosis (lowered serum bicarbonate or CO2) • Appetite suppression • Gastrointestinal disturbances (nausea, vomiting, diarrhea) • Allergic rash Life-threatening or dangerous adverse effects: • Very rarely Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis • Agranulocytosis, aplastic anemia, and other blood dyscrasias Rare and not life-threatening adverse effects: • Nephrolithiasis (secondary to decrease in urinary citrate) • Blood dyscrasias • Visual changes and transient myopia • Tinnitus • Depression • Loss of libido Weight change • Weight loss can occur

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What to do about adverse effects: • Discuss common and severe adverse effects with patients or ­parents before starting medication, including symptoms that should be reported to the physician • Discuss symptoms associated with kidney stones • Some CNS-related adverse effects may be lessened by slow titration, but they may persist at low doses despite slow titration

the epilepsy prescriber’s guide to antiepileptic drugs • Metabolic acidosis is usually compensated, but patients may be treated with oral bicarbonate for CO2 values of 15–18 mEq/L or less • If possible, acetazolamide should not be administered to patients on topiramate, zonisamide, or on the ketogenic diet, because these treatments also predispose to metabolic acidosis and to kidney stones • Patients should be encouraged to drink liberally while on aceta­ zolamide • Anorexia and weight loss may improve with dosage reduction

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Dosing and use Usual dosage range: • Adults and children over 12 years of age: 250–1000 mg/day • Children under 12 years of age: 10–20 mg/kg/day • Catamenial epilepsy: 8–30 mg/kg/day

Dosing and use

Available formulations: • Tablets: 125 mg, 250 mg • Extended release capsule: 500 mg • Parenteral solution: 500 mg powder per vial (requires reconstitution with at least 5 mL of sterile water) How to dose: • For adults and children over 12 years of age:  start treatment with 250 mg/day, once or twice daily; at intervals of 3–7 days increase as needed and as tolerated by 250 mg/day; maintenance dose generally 250 –1000  mg/day • Children under 12 years of age: start treatment with 3–6 mg/kg/day, once or twice daily; at intervals of 3–7 days increase as needed and as tolerated by 3–6 mg/kg/day; maintenance dose generally 10–20 mg/kg/day; doses of 20–30 mg/kg/day may be necessary and are well tolerated • Catamenial epilepsy: acetazolamide has been used in women with catamenial epilepsy both continuously and intermittently during the days of identified seizure exacerbation; maintenance dose generally 8–30 mg/kg/day, doses up to 1000 mg/day may be necessary and are well tolerated Dosing tips: • Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating effects • Some patients may do very well at relatively low doses of acetazolamide, such as 500 mg/day in adults or 10 mg/kg/day in children; the response to treatment should be assessed at these doses before increasing the dose further • Acetazolamide may be most effective as add-on therapy and tolerance may develop later when acetazolamide is given as adjunct therapy

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• When tolerance has developed, temporary withdrawal of acetazolamide usually restores the previous therapeutic effect • In patients with catamenial epilepsy, once an effective and welltolerated dose has been determined, this dose can be administered during the necessary number of days without gradual titration

Acetazolamide

How to withdraw drug: • May need to adjust dosage of concurrent medications as acetazolamide is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • No data are available on potential for withdrawal seizures or symptoms upon rapid discontinuation of acetazolamide; however, rapid discontinuation after chronic use may increase the risk of seizures • If possible, taper dose over a period of 1–3 months • In patients receiving intermittent treatment for a few days, such as for catamenial epilepsy, gradual tapering is usually not necessary Overdose: • To date, there have been no cases of overdose reported with acetazolamide • Severe metabolic acidosis could develop, which can usually be corrected by the administration of bicarbonate • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes acetazolamide from blood and, therefore, serves as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Serum bicarbonate (CO2) can be measured before treatment and then periodically, but it is not routine practice to do so • Other routine laboratory testing is not necessary • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at acetazolamide plasma concentrations of 10–14 mg/L (45–63 μmol/L) –– The conversion factor from mg/L to μmol/L is 4.50 (i.e., 1 mg/L = 4.50 μmol/L) –– The reference range of acetazolamide in plasma is considered to be the same for children and adults, although no data are available to support this clinical practice –– There are no data indicating the usefulness of monitoring acetazolamide by use of saliva

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Other warnings/precautions: • Patients should be monitored carefully for evidence of an allergic rash • Patients should be monitored carefully for evidence of kidney stones

the epilepsy prescriber’s guide to antiepileptic drugs • In combination with carbamazepine or oxcarbazepine, there is an increased risk of hyponatremia

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Special populations

Do not use: • Use with caution in patients undergoing treatments that are associated with an increase in risk of kidney stones, such as topiramate, zonisamide, and the ketogenic diet • Do not use in patients with hyperchloremic acidosis • Do not use in patients with cirrhosis because of the risk of severe hyperammonemia • Use with caution in patients with a history of allergic rash to another medication • A history of allergic reaction to an antibiotic sulfonamide does not appear to be an absolute contraindication for the use of acetazolamide, because there seems to be no specific crossreactivity • Long-term administration of acetazolamide is contraindicated in patients with chronic noncongestive angle-closure glaucoma • Acetazolamide should not be administered to patients receiving high-dose aspirin  – anorexia, tachypnea, lethargy, coma, and death have been reported to occur • Because of its tendency to cause potassium loss, acetazolamide is contraindicated in Addison disease and adrenal insufficiency

Special populations Renal impairment: • Acetazolamide is renally excreted, so the dose may need to be ­lowered – particularly in patients with a CrCl of < 60 mL/min; the clearance of unbound acetazolamide correlates with the ­creatinine clearance • Because acetazolamide can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of aceta­ zolamide Hepatic impairment: • Acetazolamide is not metabolized and consequently dose adjustment will not be necessary • Acetazolamide can increase hyperammonemia in patients with liver failure; the mechanism is probably increased renal tubular reabsorption of ammonium secondary to alkalinization of urine Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults

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• Age-specific higher incidence of adverse effects of acetazolamide in the pediatric age range has not been described

Acetazolamide

Elderly: • Available data on the pharmacokinetics of acetazolamide in elderly patients suggest that they have a higher unbound fraction in the plasma • The renal clearance of unbound acetazolamide is significantly lower in the elderly, and correlates with the creatinine clearance • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal and hepatic function, lower acetazolamide doses may be appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions is high Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Acetazolamide is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than acetazolamide monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of acetazolamide during pregnancy have not been identified

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Breast feeding • Breast milk: in a single case report of a mother taking 1000 mg/day of acetazolamide while breast feeding, acetazolamide concentrations in breast milk were 1.3–2.1 mg/L whereby plasma levels were 5.2–6.4 mg/L. It was calculated that the infant ingested 0.6 mg/day and the infant’s plasma levels were 0.2–0.6 mg/L. • Breastfed infants: acetazolamide plasma levels c/o above case are 4–9% of maternal plasma levels • If adverse effects are observed recommend bottle feed

the epilepsy prescriber’s guide to antiepileptic drugs The overall place of acetazolamide in the treatment of epilepsy Acetazolamide is a relatively safe drug which can be used for long periods without serious adverse effects. It is used more often as a second line add-on therapy rather than as monotherapy and in some patients dramatic effects have been observed, and a worthwhile effect has been reported widely in many patients and in differing types of seizures.

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Acetazolamide, overall role

Primary seizure types: • Absence seizures • Partial seizures Secondary seizure types: • Generalized tonic–clonic seizures • Myoclonic seizures • Juvenile myoclonic epilepsy • Catamenial epilepsy Potential advantages: • Broad spectrum of seizure protection • Rapid onset of action • Associated with few and minor pharmacokinetic interactions • Favorable adverse event profile with very rare serious adverse effects • Does not commonly exacerbate seizures Potential disadvantages: • Tolerance to the effect of acetazolamide often develops within 1–6 months • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Chapron DJ, Sweeney KR, Feig PU, Kramer PA. Influence of advanced age on the disposition of acetazolamide. British Journal of Clinical Pharmacology 1985; 19: 363–371. Forsythe WI, Owens JR, Toothill C. Effectiveness of acetazolamide in the treatment of carbamazepine-resistant epilepsy in children. Developmental Medicine and Child Neurology 1981; 23: 761–769. Holowach J, Thurston DL. A clinical evaluation of acetazolamide (Diamox) in the treatment of epilepsy in children. Journal of Pediatrics 1958; 53: 160–171. Katayama F, Miura H, Takanashi S. Long-term effectiveness and side effects of acetazolamide as an adjunct to other anticonvulsants in the treatment of refractory epilepsies. Brain and Development 2002; 24: 150–154.

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Acetazolamide 10

Lim LL, Foldvary N, Mascha E, Lee J. Acetazolamide in women with catamenial epilepsy. Epilepsia 2001; 42: 746–749. Oles KS, Penry K, Cole DLW, Howard G. Use of acetazolamide as an adjunct to carbamazepine in refractory partial seizures. Epilepsia 1989; 30: 74–78. Reiss WG, Oles KS. Acetazolamide in the treatment of seizures. Annals of Pharmacotherapy 1996; 30: 514–519. Resor SR, Resor LD. Chronic acetazolamide monotherapy in the treatment of juvenile myoclonic epilepsy. Neurology 1990; 40: 1677–1681. Soderman P, Hartvig P, Fagerlund C. Acetazolamide excretion into breast milk. British Journal of Clinical Pharmacology 1984; 17: 599–600. Tawil R, Moxley RT, Griggs RC. Acetazolamide-induced nephrolithiasis: implications for treatment of neuromuscular disorders. Neurology 1993; 43: 1105–1106. Vaziri ND, Saiki J, Barton CH, Rajudin M, Ness RL. Hemo­d ialyzability of acetazolamide. South Medical Journal 1980; 73: 422–423. Watson WA, Garrelts JC, Zinn PD, Garriott JC, McLemore TL, Clementi WA. Chronic acetazolamide intoxication. Clinical Toxicology 1984; 22: 549–563.

the epilepsy prescriber’s guide to antiepileptic drugs

ACTH Therapeutics Chemical name and structure: Adrenocorticotropic hormone, ACTH, is a peptide consisting of 39 amino acids in its natural form and 24 amino acids in its synthetic form. Its empirical formula is C207H 308O58N56S,2AcOH,32H 20.

A

Brand names: • Acortan • ACTH • Acthar • Acthelea • Cortrosyn • Synacthen • Trofocortina

Licensed indications for epilepsy: • ACTH is not licensed for the treatment of epileptic seizures

therapeutics

Generics available: • No

Licensed indications for non-epilepsy conditions: • Acute exacerbations of multiple sclerosis • Diagnostic aid in adrenocortical insufficiency • Severe muscle weakness in myasthenia gravis Nonlicensed use for epilepsy: • Infantile spasms (West syndrome) • Lennox-Gastaut syndrome • Myoclonic astatic epilepsy • Severe myoclonic epilepsy of infancy (Dravet syndrome) • Acquired epileptic aphasia (Landau-Kleffner syndrome) • Ohtahara syndrome • Rasmussen encephalitis Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • ACTH should not be considered as a standard antiepileptic treatment and should be used only for a restricted group of severe encephalopathic epilepsies as listed above Mechanism of action: • ACTH stimulates the secretion of cortisol in the adrenal gland • Is effective in patients with adrenal suppression

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• Its effect on the brain and on epilepsy may be independent of steroid secretion • ACTH suppresses the expression of corticotrophin-releasing hormone, a proconvulsant neuropeptide whose expression may be enhanced in patients with infantile spasms Efficacy profile: • The goal is elimination of spasms and suppression of the hyps­ arrhythmic pattern on the EEG • A response is often seen within the first few days of treatment • Relapse after full response and discontinuation of ACTH is not uncommon • A second course of ACTH may again be effective • In case of lack of efficacy, partial efficacy, or relapse, consider other treatments such as vigabatrin, valproic acid, topiramate, zonisamide, levetiracetam, a benzodiazepine, or vitamin B6

ACTH

Pharmacokinetics Conventional pharmacokinetic parameters do not apply to ACTH Absorption and distribution: • Because ACTH is inactivated in the gastrointestinal tract it must be administered parenterally by intramuscular injection Metabolism: • Although the precise metabolic fate of ACTH is not known, circulating ACTH is probably enzymatically cleaved at the 16–17 lysine-arginine bond by the plasma-plasminogen system Elimination: • Half-life values are considered to be ~ 15 minutes

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Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on ACTH: –– To date, there have been no reports of AEDs affecting the clearance of ACTH and affecting ACTH plasma levels • Interactions between AEDs: effects by ACTH: –– To date, there have been no reports of ACTH affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs: effects on ACTH: –– To date, there have been no reports of other non-AED drugs affecting the clearance of ACTH and affecting ACTH plasma levels

the epilepsy prescriber’s guide to antiepileptic drugs • Interactions between AEDs and non-AED drugs: effects by ACTH: –– To date, there have been no reports of ACTH affecting the clearance of other non-AED drugs and affecting their plasma levels

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Pharmacodynamic drug interactions: • To date, none have been identified Hormonal contraception: • The effect of ACTH on hormonal contraception is unknown, but ACTH is virtually never administered to women of childbearing age

Common adverse effects: • Irritability, at times severe • Cushingoid features • Hypertension • Hyperglycemia, glycosuria • Electrolyte imbalances

Adverse effects

Adverse effects How drug causes adverse effects: • Most adverse effects of ACTH are shared by steroids and are likely to be related to the stimulation of cortisol secretion by the adrenal gland

Life-threatening or dangerous adverse effects: • Immunosuppression and possibly impaired function of polymorphonuclear leukocytes • Pneumonia, in particular pneumocystis pneumoniae • Sepsis • Congestive heart failure Rare and not life-threatening adverse effects: • Brain atrophy • Peptic ulcer • Subaortic hypertrophic cardiomyopathy • Cataracts • Glaucoma • Seizure exacerbation Weight change: • Weight gain is common, as part of the cushingoid features What to do about adverse effects: • Discuss common and severe adverse effects with parents before starting medication, including symptoms that should be reported to the physician

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• Always start ACTH treatment in the hospital • ACTH is contraindicated in the presence of serious bacterial or viral infection such as tuberculosis, varicella, or cytomegalovirus • Prophylaxis of pneumocystis pneumonia with trimethoprim­sulfamethoxazole may be considered • Elevated blood pressure may require treatment, initially mostly with a diuretic

ACTH

Dosing and use Usual dosage range: • The optimal dosage (calculated in IU/m 2 body surface/day) and schedule have not been determined • The highest dose is usually given at the onset, followed by a gradual tapering until discontinuation • The initial dose used most commonly is 150 IU/m 2/day given in two divided doses, with a range between 85 and 250 IU/m 2/day; this is given for 1–2 weeks and the dose is then tapered gradually to achieve a total treatment duration of 4–6 weeks Available formulations: • Corticotropin (porcine pituitary extract, 39 amino acids, shortacting) –– Gel 80 IU/mL 100 IU = 0.72 mg –– Lyophylized powder 100 IU = 0.72 mg • Cosyntropin/Tetracosactrin (synthetic, 24 amino acids, short-acting) –– 100 IU = 1.0 mg • Cosyntropin/Tetracosactrin (synthetic, 24 amino acids, long-acting) –– 100 IU = 2.5 mg How to dose: • ACTH is administered intramuscularly as a treatment course for a limited amount of time, usually a few weeks • A typical (but not exclusive) dosage schedule would consist of a 4-week course, with 150 IU/m 2/day given in two divided doses for 2 weeks, 30 IU/m 2/day for 3 days, 15 IU/m 2/day for 3 days, 10 IU/ m 2/day for 3 days, then 10 IU/m 2 every other day for three doses; other schedules may consist of a somewhat longer tapering period

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Dosing tips: • Treatment with ACTH is always initiated in the hospital for three main reasons: –– It is essential to undertake a baseline clinical and laboratory assessment of the patient –– Enables observation of early significant adverse effects

the epilepsy prescriber’s guide to antiepileptic drugs –– Allows the teaching of intramuscular administration to parents and/or carers

Overdose: • Doses of ACTH greater than 250 IU/m 2/day are commonly associated with serious and at times fatal complications that do not differ from those described under the adverse effects section Tests and therapeutic drug monitoring: • Before initiation of ACTH therapy: –– Place a PPD (purified protein derivative) skin test to rule out tuberculosis –– Obtain chest x-ray in the presence of symptoms of respiratory illness –– Do not administer any immunization for 10 days before and during treatment with ACTH –– Vital signs, including blood pressure –– Physical examination to exclude evidence of infection –– Test urine for glucose and for evidence of urinary infection –– Test stool for blood (guaiac) –– Blood for CBC (complete blood count), electrolytes, BUN (blood urea nitrogen), Cr, Ca, Mg, phosphate –– Consider baseline echocardiogram • During ACTH therapy: –– Blood pressure daily for 1 week, then three times weekly until ACTH discontinuation –– Test urine for glucose twice weekly –– Test stool for blood (guaiac) –– Prescribe an H 2 antagonist, especially if stool is guaiac positive –– Blood for CBC, electrolytes, Cr, Ca, Mg, phosphate after 2–4 weeks –– Consider follow-up echocardiogram after 2–4 weeks (hypertrophic cardiomyopathy) –– Patient should be examined if fever develops

Dosing and use

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as ACTH is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • All schedules for the administration of ACTH consist of a limited course with a predetermined withdrawal phase • ACTH should never be stopped abruptly because it suppresses endogenous ACTH secretion • The purpose of the tapering phase is to gradually restore normal endogenous ACTH secretion • Monitoring of morning levels of cortisol may be useful during withdrawal

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Other warnings/precautions: Patients should be monitored carefully for evidence of infection • ACTH may accentuate electrolyte loss associated with diuretic therapy Do not use: • ACTH is contraindicated in the presence of serious bacterial or viral infection such as tuberculosis, varicella, or cytomegalovirus Special populations Renal impairment: • There is no evidence that renal impairment requires changes in ACTH doses Hepatic impairment: • There is no evidence that hepatic impairment requires changes in ACTH doses

ACTH

Children: • ACTH for the treatment of epilepsy is used almost exclusively in children Elderly: • It is very unlikely that ACTH would ever be used in elderly patients for the treatment of seizures Pregnancy: • It is very unlikely that ACTH would ever be used in a pregnant patient for the treatment of seizures • ACTH is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] Breast feeding • It is very unlikely that ACTH would ever be used in a nursing mother for the treatment of seizures

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The overall place of ACTH in the treatment of epilepsy ACTH is used for the treatment of infantile spasms (West syndrome), a condition consisting of infantile spasms, disturbed psychomotor development and the characteristic EEG pattern of hypsarrhythmia. ACTH has an all or nothing effect and typically in 70–75% of children total seizure suppression occurs. In those children that do not respond to ACTH other medications should be considered including vigabatrin, valproic acid, topiramate, zonisamide, levetiracetam, a benzodiazepine, or vitamin B6.

the epilepsy prescriber’s guide to antiepileptic drugs Primary seizure types: • Infantile spasms (West syndrome)

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Secondary seizure types: • Lennox-Gastaut syndrome • Myoclonic astatic epilepsy • Severe myoclonic epilepsy of infancy (Dravet syndrome) • Acquired epileptic aphasia (Landau-Kleffner syndrome) • Ohtahara syndrome • Rasmussen encephalitis

Potential disadvantages: • ACTH has several potentially serious or even life-threatening adverse effects

Suggested reading Baram TZ, Mitchell WG, Tournay A, Snead OC, Hanson RA, Horton EJ . High-dose corticotropin (ACTH) versus prednisone for infantile spasms:  a prospective, randomized, blinded study. Pediatrics 1996; 97: 375–379. Hrachovy RA, Frost JD, Kellaway P, Zion TE. Double-blind study of ACTH vs prednisolone therapy in infantile spasms. Journal of Pediatrics 1983; 103: 641–645. Kivity S, Lerman P, Ariel R, Danziger Y, Mimouni M, Shinnar S. Long-term cognitive outcomes of a cohort of children with cryptogenic infantile spasms treated with high-dose adrenocorticotropic hormone. Epilepsia 2004; 45: 255–262. Lux AL, Edwards SW, Hancock E, Johnson AL, Kennedy CR, Newton RW, O’Callaghan FJ, Verity CM, Osborne JP; United Kingdom Infantile Spasms Study. The United Kingdom Infantile Spasms Study (UKISS) comparing hormone treatment with vigabatrin on developmental and epilepsy outcomes to age 14 months: a multicentre randomized trial. Lancet Neurology 2005; 4: 712–717. Mackay MT, Weiss SK, Adams-Webber T, Ashwal S, Stephens D, Ballaban-Gill K, Baram TZ, Duchowny M, Hirtz D, Pellock JM, Shields WD, Shinnar S, Wyllie E, Snead OC III; American Academy of Neurology; Child Neurology Society. Practice parameter: medical treatment of infantile spasms: report of the American Academy of Neurology and the Child Neurology Society. Neurology 2004; 62: 1668–1681.

acth, overall role

Potential advantages: • ACTH has the best documented evidence of efficacy in the treatment of infantile spasms • A single course of 4–6 weeks of ACTH treatment can have a longlasting or permanent anticonvulsant effect

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ACTH 18

Maekawa K, Ohta H, Tamai I. Transient brain shrinkage in infantile spasms after ACTH treatment. Report of two cases. Neuropaediatrie 1980; 11: 80–84. Tacke E, Kupferschmid C, Lang D. Hypertrophic cardiomyopathy during ACTH treatment. Klinka Padiatrika 1983; 195: 124–128. Vigevano F, Cilio MR. Vigabatrin versus ACTH as first-line treatment for infantile spasms:  a randomized, prospective study. Epilepsia 1997; 38: 1270–1274.

the epilepsy prescriber’s guide to antiepileptic drugs

Carbamazepine Therapeutics Chemical name and structure: Carbamazepine, 5H-dibenz[b,f ]azepine-5-carboxamide, is a white or yellowish-white, crystalline powder, with a molecular weight of 236.27 and an empirical formula of C15H12N2O.

C

N O

NH2

therapeutics

Brand names: • Actebral; Actebral Retard; Actinerval; Amizepin; Apo-Carbama­ zepine; Azepal • Bamgetol; Basitrol; Brucarcer • Carba; Carbagen SR; Carbatrol; Camapine; Carazepin; Carbabeta; Carbadac; Carbalex; Carbamazepin-B; Carbapsy; Carbatol; Carbatol CR; Carbazene; Carbazep; Carbazina; Carmapine; Carmaz; Carmian; Carmine; Carpin; Carzepin; Carzepine; Clostedal • Degranol • Elpenor; Epazin; Epazin; Epikor; Epileptol; Epileptol CR; Eposal Retard; Espa-lepsin • Finlepsin • Gericarb SR • Hermolepsin • Karbamazepin • Lepsitol • Neugeron; Neurolep; Neurotol; Neurotop; Neurotop Retard • Panitol • Sepibest; Sirtal; Stazepine • Taver; Tegol; Tegral; Tegretal; Tegretol; Tegretol CR; Tegretol Retard; Temporol; Teril-CR; Timonil; Timonil Retard; Trepina • Vulsivan • Zeptol CR Generics available: • Yes Licensed indications for epilepsy: • Partial and secondary generalized seizures (UK-SPC; FDA-PI) • Primary generalized tonic–clonic seizures (UK-SPC; FDA-PI)

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the epilepsy prescriber’s guide to antiepileptic drugs

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Licensed indications for non-epilepsy conditions: • Trigeminal neuralgia (UK-SPC; FDA-PI) • Bipolar disorder unresponsive to lithium (UK-SPC) Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • There are none

Carbamazepine

Ineffective (contraindicated): • Juvenile myoclonic epilepsy • Juvenile absence epilepsy • Epileptic encephalopathies (e.g., Lennox-Gastaut syndrome) • Neonatal and febrile seizures • Exaggerates myoclonic jerks, absences, and atonic seizures Mechanism of action: • Acts as a use-dependent blocker of voltage-sensitive sodium channels • Inhibits L-type calcium channels • Inhibits release of glutamate • Has a moderate anticholinergic action which is responsible for some of its adverse effects Efficacy profile: • The goal of treatment is complete remission of seizures • Continue treatment until all symptoms are gone or until improvement is stable and then continue treating indefinitely as long as improvement persists • Continue treatment indefinitely to avoid recurrence of seizures • If carbamazepine is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: 75–85% • Food co-ingestion: neither delays the rate of absorption nor reduces the extent of absorption • Tmax: 2–9 hours (immediate release tablets); 1–7 hours (chewable tablets); 0.5–4 hours (liquid suspensions). Extended release formulations have prolonged Tmax values • Time to steady state: 2–4 days (adults); 2–3 days (children) • Pharmacokinetics: nonlinear due to autoinduction • Protein binding: 75%

the epilepsy prescriber’s guide to antiepileptic drugs • Volume of distribution: 0.8–2.0 L/kg • Salivary concentrations: carbamazepine is secreted into saliva and concentrations are similar to the unbound levels seen in plasma

Elimination: • Following a single dose, half-life values in adults and children are 18–55 hours and 3–32 hours, respectively • During maintenance carbamazepine monotherapy half-life values in adults and children are 8–20 hours and 10–13 hours, respectively • In the elderly carbamazepine half-life values are 30–50 hours • Half-life of carbamazepine-10,11-epoxide is ~34 hours • Renal excretion:  <2% of an administered dose is excreted unchanged in urine

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on carbamazepine: –– Felbamate, oxcarbazepine, phenobarbital, phenytoin, and primidone can increase the clearance of carbamazepine and decrease carbamazepine plasma levels –– Stiripentol can decrease the clearance of carbamazepine and increase carbamazepine plasma levels –– Valproic acid can inhibit the metabolism of epoxide hydrolase and increase carbamazepine-10,11-epoxide plasma levels • Interactions between AEDs: effects by carbamazepine: –– Carbamazepine can decrease plasma levels of clobazam, clonazepam, ethosuximide, felbamate, lamotrigine, methsuximide, oxcarbazepine, phenytoin, primidone, rufinamide, stiripentol, tiagabine, topiramate, valproic acid, and zonisamide • Interactions between AEDs and non-AED drugs:  effects on carbamazepine: –– Cimetidine, clarithromycin, danazol, delavirdine, diltiazem, erythromycin, fluoxetine, fluconazole, fluvoxamine, gemfibrozil, haloperidol, indinavir, isoniazid, josamycin, ketoconazole,

Drug interaction profile

Metabolism: • Metabolized in the liver, primarily by CYP3A4 with some contribution by CYP2C8, to carbamazepine-10,11-epoxide, which is pharmacologically active • Carbamazepine-10,11-epoxide is in turn metabolized, by means of epoxide hydrolase, to an inactive trans carbamazepine diol • Carbamazepine undergoes autoinduction so that clearance can increase three-fold within several weeks of starting therapy and this often requires an upward dosage adjustment

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the epilepsy prescriber’s guide to antiepileptic drugs

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Carbamazepine

metronidazole, nefazodone, propoxyphene, ritonavir, ticlopidine, trazodone, troleandomycin, verapamil, and viloxazine can increase carbamazepine plasma levels –– Efavirenz, nevirapine, rifampicin, and St John’s wort can decrease carbamazepine plasma levels • Interactions between AEDs and non-AED drugs:  effects by carbamazepine: –– Carbamazepine can increase plasma levels of verapamil –– Carbamazepine can decrease plasma levels of acetaminophen, albendazole, amiodarone, amitriptyline, benzodiazepines, bupropion, citalopram, clomipramine, clozipine, cortisol, cyclosporin, delavirdine, desipramine, dexamethasone, dicoumarol, doxepin, doxycycline, efavirenz, erythromycin, felodipine, fluphenazine, haloperidol, imipramine, indinavir, itraconazole, ketoconazole, mebendazole, methotrexate, methylprednisolone, mianserin, mirtazapine, nefazodone, nelfinavir, nevirapine, nimodipine, nivadipine, nortriptyline, olanzapine, omeprazole, paclitaxel, paroxetine, phenprocoumon, praziquantel, prednisolone, protriptyline, quetiapine, risperidone, ritonavir, saquinavir, sertraline, teniposide, theophylline, thioridazine, vincristine, warfarin, zidovudine, and ziprasidone Pharmacodynamic drug interactions: • Co-medication with lamotrigine:  neurotoxicity may present as headache, nausea, diplopia, and ataxia – this occurs in the absence of any change in lamotrigine, carbamazepine, or carbamazepineepoxide plasma levels • Co-medication with levetiracetam: neurotoxicity may present as nystagmus, diplopia, ataxia, nausea, and vomiting  – this occurs in the absence of any change in levetiracetam, carbamazepine, or carbamazepine-epoxide plasma levels Hormonal contraception: • Carbamazepine enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking carbamazepine

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Adverse effects How drug causes adverse effects: • CNS adverse effects theoretically due to excessive actions at voltage-sensitive sodium channels • Major pharmacologically active metabolites (carbamazepine-10, 11-epoxide) may be the cause of many adverse effects • Mild anticholinergic effects may contribute to sedation and blurred vision

the epilepsy prescriber’s guide to antiepileptic drugs Common adverse effects: • Sedation, dizziness, confusion, unsteadiness, headache • Nausea, vomiting, diarrhea • Blurred vision • Benign leukopenia (transient; in up to 10%) • Hyponatremia, neutropenia • Rash

Adverse effects

Life-threatening or dangerous adverse effects: • Rare aplastic anemia, agranulocytosis (unusual bleeding or bruising, mouth sores, infections, fever, sore throat) • Rare severe dermatologic reactions (Stevens-Johnson syndrome) • Rare cardiac problems (e.g., bradycardia, arrhythmia, atrioventricular block) • Rare induction of psychosis or mania • SIADH (syndrome of inappropriate antidiuretic hormone secretion) with hyponatremia • Increased frequency of generalized convulsions (in patients with atypical absence seizures) • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with carbamazepine; can be prevented by administration of vitamin K to the mother before delivery

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Rare and not life-threatening adverse effects: • Aseptic meningitis accompanied by myoclonus and peripheral eosinophilia • Anaphylactic reaction • Angioneurotic edema • Osteomalacia/osteoporosis • Taste disturbances • Arthralgia, muscle pain, muscle spasm Weight change • Not usual; weight gain could be related to water retention, however, increased appetite and increased weight without edema can also occur What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Risk of serious adverse effects is greatest in the first few months of treatment • CNS-related adverse effects are usually dose-dependent, are reversible and are prevented by slow and upward titration following initiation of treatment • Common adverse effects such as sedation often abate after a few months

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the epilepsy prescriber’s guide to antiepileptic drugs

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• Take with food or split dose to avoid gastrointestinal effects • Switch to extended release carbamazepine because dosage frequency as well as sedation, diplopia, confusion, and ataxia may be reduced • Extended release carbamazepine can be sprinkled on soft food Dosing and use Usual dosage range: • Adults and children over 12 years of age: 800–1200 mg/day • Children 6–12 years of age: 600–1000 mg/day • Children under 6 years of age: 30–40 mg/kg/day

Carbamazepine 24

Available formulations: • Tablets: 100 mg, 200 mg, 400 mg • Chewable tablets: 100 mg, 200 mg • Liquid (oral suspension): 300 mL, 450 mL (100 mg/5 mL) • Suppositories: 125 mg, 250 mg • Extended release tablets: 100 mg, 200 mg, 400 mg • Extended release capsules: 200 mg, 300 mg How to dose: • When initiating carbamazepine treatment start with a low dose and titrate slowly so as to minimize adverse effects. –– For adults and children over 12 years of age: start treatment with 200 mg twice daily (tablet) or 1 teaspoon (100 mg) four times a day (suspension); each week increase by up to 200 mg/day in divided doses (two doses for extended release formulation, three–four doses for other tablets); maintenance dose generally 800–1200 mg/ day for adults; some patients may require up to 1600 mg/day. –– Children 6–12 years old: start treatment with 100 mg/day twice daily or 0.5 teaspoon (50 mg) four times a day (suspension) and increase at weekly intervals in increments of 100 mg/day in divided doses (two doses for extended release formulation, three– four doses for all other formulations); maximum dose generally 1000 mg/day; maintenance dose generally 600–1000 mg/day –– Children under 6 years: start treatment with 5–10 mg/kg/day in two or three divided doses for tablet formulations (four doses for suspension) and increase at weekly intervals in increments of 5–10 mg/kg/day; maintenance dose of 30 mg/kg/day or more is often required and dosage requirement increase two-fold in children co-prescribed enzyme-inducing antiepileptic drugs Dosing tips: • Higher peak plasma levels occur with the suspension formulation than with the same dose of the tablet formulation, so suspension should generally be started at a lower dose and titrated slowly

the epilepsy prescriber’s guide to antiepileptic drugs

How to withdraw drug: • May need to adjust dosage of concurrent medications as carbamazepine is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Rapid discontinuation may increase the risk of seizures

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Dosing and use

• Take carbamazepine with food to avoid gastrointestinal effects • Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating effects • Should titrate slowly in the presence of other sedating agents, such as other antiepileptic drugs to best tolerate additive sedative adverse effects • Can sometimes minimize the impact of carbamazepine upon the bone marrow by dosing slowly and monitoring closely when initiating treatment; initial trend to leukopenia/neutropenia may reverse with continued conservative dosing over time and allow subsequent dosage increases with careful monitoring • Carbamazepine often requires a dosage adjustment upward with time, as the drug induces its own metabolism, thus lowering its own plasma levels over the first several weeks to months of treatment • Do not break or chew carbamazepine extended release tablets as this will alter the controlled release properties • Generally higher doses of the extended release formulations are possible (because of the reduction in diurnal changes in plasma carbamazepine blood levels) resulting in better seizure control and reduced intermittent diurnal adverse effects

Overdose: • Can be fatal (lowest known fatal dose in adults is 3.2 g, in adolescents is 4 g, and in children is 1.6 g): symptoms include nausea, vomiting, involuntary movements, urinary retention, trouble breathing, sedation, coma • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes carbamazepine from blood and, therefore, serves as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Before starting: blood count, liver, kidney, and thyroid function tests • During treatment: blood count every 2 weeks for 2 months, then every 3 months throughout treatment • During treatment: liver, kidney, and thyroid function tests every 6–12 months. Consider monitoring sodium levels because of possibility of hyponatremia 25

the epilepsy prescriber’s guide to antiepileptic drugs

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Carbamazepine 26

• Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at carbamazepine plasma concentrations of 4–12 mg/L (17–51 μmol/L) –– The conversion factor from mg/L to μmol/L is 4.23 (i.e., 1 mg/L = 4.23 μmol/L) –– Because children metabolize carbamazepine more rapidly, resulting in carbamazepine-10,11-epoxide levels approaching those of carbamazepine, carbamazepine-10,11-epoxide makes a greater contribution to the pharmacological effects (both beneficial and toxic) of carbamazepine in children than in adults –– The upper boundary of the reference range for carbamazepine10,11-epoxide is 9 μmol/L –– The conversion factor from mg to μmol is 3.96 (i.e., 1 mg/L = 3.96 μmol/L) –– The reference range of carbamazepine in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Carbamazepine can be monitored by use of saliva, which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant Other warnings/precautions: • Patients should be monitored carefully for signs of unusual bleeding or bruising, mouth sores, infections, fever, or sore throat, as the risk of aplastic anemia and agranulocytosis with carbamazepine use is five– eight times greater than in the general population (risk in the untreated general population is 6 patients per 1 million per year for agranulocytosis and 2 patients per 1 million per year for aplastic anemia) • Because carbamazepine has a tricyclic chemical structure, it is not recommended to be taken with MAOIs, including 14 days after MAOIs are stopped; do not start an MAOI until 2 weeks after discontinuing carbamazepine • May exacerbate narrow angle-closure glaucoma • May need to restrict fluid intake because of risk of developing syndrome of inappropriate antidiuretic hormone secretion, hyponatremia and its complications • Use with caution in patients with mixed seizure disorders that include atypical absence seizures because carbamazepine has been associated with increased frequency of generalized convulsions in such patients Do not use: • If patient has a proven allergy to tricyclic compounds • If patient has a proven allergy to carbamazepine, oxcarbazepine or eslicarbazepine acetate • If a patient has bone marrow suppression • If a patient is taking an MAOI

the epilepsy prescriber’s guide to antiepileptic drugs Special populations Renal impairment: • Carbamazepine is renally secreted, therefore, the dose may need to be lowered • Because carbamazepine can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of carbamazepine

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Hepatic impairment: • Carbamazepine is extensively metabolized in the liver and consequently lower doses may be required

Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal and hepatic function, lower carbamazepine doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with carbamazepine is substantial Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Carbamazepine is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy] • Use during first trimester may raise risk of neural tube defects (e.g., spina bifida) or other congenital anomalies • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • If drug is continued, start on folate 1 mg/day early in pregnancy to reduce risk of neural tube defects • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than carbamazepine monotherapy

Special populations

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

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the epilepsy prescriber’s guide to antiepileptic drugs

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• Taper drug if discontinuing • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with carbamazepine; can be prevented by administration of vitamin K to the mother before delivery • Seizures, even mild seizures, may cause harm to the embryo/ fetus • Data on the pharmacokinetic changes of carbamazepine during pregnancy are conflicting; carbamazepine clearance can increase by up to 20% during pregnancy, accompanied by a decrease in the total plasma concentration of up to 42% and a 22% decrease in the free (nonprotein bound) concentration

Carbamazepine

Breast feeding • Breast milk:  carbamazepine: 10–30% of maternal plasma levels; carbamazepine-10,11-epoxide: 50% of maternal plasma levels • Breastfed infants:  carbamazepine plasma levels are 10–20% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects, including hematological effects • Recommend bottle feed particularly if infant shows signs of irritability or sedation • Some cases of neonatal seizures, respiratory depression, vomiting, and diarrhea have been reported in infants whose mothers received carbamazepine during pregnancy

The overall place of carbamazepine in the treatment of epilepsy Carbamazepine is particularly effective for the treatment of focal epilepsies (idiopathic or symptomatic) with or without secondarily generalized tonic–clonic seizures. It is also effective in primary generalized tonic–clonic seizures. Comparative studies show that carbamazepine is superior to other antiepileptic drugs (e.g., phenytoin, phenobarbital and primidone) and of the newer antiepileptic drugs only levetiracetam may have similar efficacy. However, carbamazepine is ineffective in neonatal or febrile seizures and is contraindicated and ineffective in idiopathic generalized epilepsies and epileptic encephalopathies. Primary seizure types: • Focal epilepsies of any type (idiopathic or symptomatic) with or without secondarily generalized tonic–clonic seizures • Primary generalized tonic–clonic seizures

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Secondary seizure types: • None

the epilepsy prescriber’s guide to antiepileptic drugs

Potential disadvantages: • Idiosyncratic and other adverse effects • Requires frequent blood testing and close monitoring • Pharmacokinetics are not linear due to autoinduction • Associated with significant pharmacokinetic interactions and usually acts as an inducer of drug metabolism • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Callaghan N, Kenny RA, O’Neil B, Crowley M, Goggin T. A prospective study between carbamazepine, phenytoin and sodium valproate as monotherapy in previously untreated and recently diagnosed patients with epilepsy. Journal of Neurology, Neurosurgery, and Psychiatry 1985; 48: 639–644. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotheropeutics 2010; 10: 119–140. Mattson RH, Cramer JA, Collins JF. A comparison of valproate with carbamazepine for the treatment of complex partial seizures and secondarily generalized tonic-clonic seizures in adults. The Department of Veterans Affairs Epilepsy Cooperative Study. New England Journal of Medicine 1992; 327: 765–771. Patsalos PN, Berry DJ, Bourgeois BFD, Cloyd JC, Glauser TA, Johannessen SI, Leppik IE, Tomson T, Perucca E. Antiepileptic drugs – Best practice guidelines for therapeutic drug monitoring:  a position paper by the Subcommission on Therapeutic Drug Monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia 2008; 49: 1239–1276. Patsalos PN, Froscher W, Pisani F, van Rijn CM. The importance of drug interactions in epilepsy therapy. Epilepsia 2002; 43: 365–385.

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Carbamazepine, overall role

Potential advantages: • Carbamazepine is a particularly good antiepileptic drug for the treatment of focal epilepsies of any type (idiopathic or symptomatic) with or without secondarily generalized tonic–clonic seizures • Also effective in primary generalized tonic–clonic seizures • In numerous comparative studies, no other antiepileptic drug showed better efficacy than carbamazepine in focal seizures although some of the new antiepileptic drugs are better tolerated • Contrary to previous studies, a recent pregnancy register found that the risk of teratogenicity is small – monotherapy serious malformation rates are 2.3% versus 2.4% for no antiepileptic drug

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Carbamazepine 30

Patsalos PN, Krishna S, Elyas AA, Lascelles PT. Carbamazepine and carbamazepine-10,11-epoxide pharmacokinetics in an overdose patient. Human Toxicology 1987; 6: 241–244. Patsalos PN, Perucca E. Clinically important interactions in epilepsy:  general features and interactions between antiepileptic drugs. Lancet Neurology 2003; 2: 347–356. Patsalos PN, Perucca E. Clinically important interactions in epilepsy: interactions between antiepileptic drugs and other drugs. Lancet Neurology 2003; 2: 473–481. Rambeck B, Salke-Treumann A, May T, Boenigh HE. Valproic acid induced carbamazepine-10,11-epoxide toxicity in children and adolescents. European Neurology 1990; 30: 79–83. Sisodiya SM, Sander JWAS, Patsalos PN. Carbamazepine toxicity during combination therapy with levetiracetam: a pharmacodynamic interaction. Epilepsy Research 2002; 48: 217–219.

the epilepsy prescriber’s guide to antiepileptic drugs

Clobazam Therapeutics Chemical name and structure: Clobazam,   7-chloro-1-methyl-5-phenyl-1,5-benzodiazepine-2, 4-dione, is a white crystalline powder, with a molecular weight of 300.74 and an empirical formula of C16H13Cl 2O2 . H

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O

N

Cl

N O

therapeutics

Brand names: • Asabium • Castilium; Clarmyl; Clobamax; Clobazan; Clopax • Frisium • Grifoclobam • Karidium • Lucium • Noiafren • Sederlona • Urbadan; Urbanil; Urbanol; Urbanyl Generics available: • Yes Licensed indications for epilepsy: • Adjunctive intermittent therapy of partial or generalized seizures in patients > 3 years of age (UK-SPC) • Nonconvulsive status epilepticus (UK-SPC) Licensed indications for non-epilepsy conditions: • Anxiolytic (UK-SPC) Nonlicensed use for epilepsy: • Reading epilepsy • Febrile seizures • Catamenial epilepsy

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the epilepsy prescriber’s guide to antiepileptic drugs

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• Lennox-Gastaut syndrome • Startle epilepsy • Alcohol withdrawal seizures • Benign childhood partial epilepsies Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Data on seizure contraindications are not available Mechanism of action: • Binds to benzodiazepine receptors at the GABA-A ligand-gated chloride channel complex • Enhances the inhibitory effects of GABA • Boosts chloride conductance through GABA-regulated channels

Clobazam

Efficacy profile: • Clobazam is commonly combined with other antiepileptic drugs for the treatment of seizures • The goal of treatment is complete remission of seizures • Onset of action may occur within the first few days • Continue treatment until all symptoms are gone or until improvement is stable and then continue treating indefinitely as long as improvement persists • Continue treatment indefinitely to avoid recurrence of seizures • If clobazam is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome Pharmacokinetics Absorption and distribution: • Oral bioavailability: > 95% • Food co-ingestion:  does not affect the extent of absorption but does slow the rate of absorption • Tmax: 1–3 hours • Time to steady state: 2–7 days (7–10 days if the pharmacologically active N-desmethylclobazam metabolite is included) • Pharmacokinetics: linear • Protein binding: 85% • Volume of distribution: 0.87–1.83 L/kg • Salivary concentrations: clobazam and N-desmethylclobazam are secreted into saliva and concentrations are similar to the unbound levels seen in plasma

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Metabolism: • Metabolized in the liver, primarily by desmethylation, to N-desmethylclobazam which is pharmacologically active

the epilepsy prescriber’s guide to antiepileptic drugs • Clobazam also undergoes metabolism by hydroxylation to form other metabolites, namely 4-hydroxyclobazam and 4-hydroxy desmethylclobazam • The N-desmethylclobazam metabolite contributes significantly to the efficacy of clobazam • Autoinduction is not a feature of clobazam metabolism

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on clobazam: –– Carbamazepine, phenobarbital, phenytoin, and primidone can increase the clearance of clobazam and decrease clobazam plasma levels; concurrently N-desmethylclobazam plasma levels are also increased –– Felbamate can decrease the clearance of clobazam and increase clobazam plasma levels; concurrently N-desmethylclobazam plasma levels are also increased –– Stiripentol can decrease the clearance of clobazam and, more potently, of N-desmethylclobazam and it increases clobazam plasma levels and N-desmethylclobazam plasma levels severalfold • Interactions between AEDs: effects by clobazam: –– Clobazam can increase plasma levels of phenytoin, primidone, and valproic acid • Interactions between AEDs and non-AED drugs:  effects on clobazam: –– Cimetidine can increase clobazam plasma levels but has no effect on N-desmethylclobazam plasma levels • Interactions between AEDs and non-AED drugs:  effects by clobazam: –– To date, there have been no reports of clobazam affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • Clobazam can potentiate the effects of CNS depressants such as alcohol, barbiturates, and neuroleptics

Drug interaction profile

Elimination: • Elimination half-life values for clobazam in adults are 10–30 hours • Elimination half-life values for N-desmethylclobazam in adults are 36–46 hours • In children clobazam half-life values are ~16 hours • In the elderly clobazam half-life values are 30–48 hours • Renal excretion:  the excreted unchanged clobazam in urine is insignificant

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the epilepsy prescriber’s guide to antiepileptic drugs

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Hormonal contraception: • Clobazam does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control Adverse effects How drug causes adverse effects: • Same mechanism for adverse effects as for therapeutic effects  – namely due to excessive actions at benzodiazepine receptors • Long-term adaptations in benzodiazepine receptors may explain the development of dependence, tolerance, and withdrawal • Adverse effects are generally immediate, but immediate adverse effects often disappear in time • Major metabolite (N-desmethylclobazam) may contribute to the observed adverse effects

Clobazam

Common adverse effects: • Sedation (sometimes intolerably severe) • Drowsiness, fatigue • Hyposalivation, dryness of mouth • Loss of appetite, constipation • Behavioral and cognitive impairment • Restlessness, aggressiveness, coordination disturbances • Severe aggressive outbursts, hyperactivity, insomnia, and depression with suicidal ideation may occur, particularly in children • Physical dependence characterized by a withdrawal syndrome when the drug is withdrawn – physical dependence develops more rapidly with larger doses Life-threatening or dangerous adverse effects: • Withdrawal syndrome in chronic use • Respiratory depression, especially at high doses and when taken with CNS depressants in overdose Rare and not life-threatening adverse effects: • Amnesia accompanied by inappropriate behavior • Hallucination, nightmare • Unsteadiness of gait • Nystagmus • Loss of libido Weight change: • Not common

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What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician

the epilepsy prescriber’s guide to antiepileptic drugs • Lower the dose • Somnolence may be partly prevented by administering the drug in small doses 1 hour before sleep

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Dosing and use Usual dosage range: • Adults and children over 12 years of age: 20–40 mg/day • Children under 12 years of age: 0.4–0.8 mg/kg/day Available formulations: • Tablets: 10 mg • Capsules: 10 mg

Dosing and use

How to dose: • When initiating clobazam treatment start with a low dose and titrate slowly so as to minimize adverse effects. –– For adults and children over 12 years of age:  start treatment with 5–10  mg/day at night and increase at weekly intervals in increments of 5 mg/day up to a total of 40 mg/day –– Children under 12 years of age: start treatment with 0.1–0.2 mg/ kg/day and slowly increase in weekly intervals in increments of 0.1 mg/kg/day up to a total of 0.8 mg/kg/day Dosing tips: • Administer as adjunctive therapy in all drug-resistant epilepsies at a dose of 20–30 mg nocte – half this dose in children < 5 years old • Twice a day dosing is fine – smaller dose should be ingested in the day with the larger dose just before sleep • Tolerance may develop but more than a third of patients do not develop tolerance • When clobazam is effective, most patients continue to benefit for years without drug dependence or unwanted adverse effects How to withdraw drug: • May need to adjust dosage of concurrent medications as clobazam is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Withdrawal should be very slow, occurring over 4–6 months • Rapid discontinuation often leads to withdrawal symptoms, ­seizures and status epilepticus Overdose: • To date, there have been no cases of overdose reported with clobazam • The stomach should be emptied immediately by lavage or by induction of emesis

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• Treatment of overdose consists of supportive care and the administration of the benzodiazepine receptor antagonist flumazenil • It is not known whether hemodialysis removes clobazam from blood and, therefore, would serve as a useful procedure in cases of overdose

Clobazam

Tests and therapeutic drug monitoring: • During treatment:  periodic liver tests and blood counts may be prudent • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at clobazam plasma concentrations of ­0.03–0.30 mg/L (0.1–1.0 μmol/L) –– The conversion factor from mg/L to μmol/L is 3.33 (i.e., 1 mg/L = 3.33 μmol/L) –– The reference range for N-desmethylclobazam is 0.30–3.00 mg/L (1–10 μmol/L) –– The conversion factor from mg/L to μmol/L is 3.49 (i.e., 1 mg/L = 3.49 μmol/L) –– The reference ranges of clobazam and N-desmethylclobazam in plasma are considered to be the same for children and adults although no data are available to support this clinical practice –– Clobazam and N-desmethylclobazam can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant Other warnings/precautions: • Use with caution in patients with pulmonary disease; rare reports of death after initiation of benzodiazepines in patients with severe pulmonary impairment • Use only with extreme caution if patient has obstructive sleep apnea • Some depressed patients may experience a worsening of suicidal ideation • Some patients may exhibit abnormal thinking or behavioral changes similar to those caused by other CNS depressants (i.e., either depressant actions or disinhibiting actions) • Clobazam is a Schedule IV drug and the risk of dependence may increase with dose and duration of treatment

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Do not use: • If patient has respiratory depression • If patient has acute pulmonary insufficiency • If patient has sleep apnea syndrome • If patient has marked neuromuscular respiratory weakness, including unstable myasthenia gravis • If patient has severe liver disease • If there is a proven allergy to clobazam or any other benzodiazepine

the epilepsy prescriber’s guide to antiepileptic drugs Special populations Renal impairment: • Clobazam is renally secreted, so the dose may need to be lowered

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Hepatic impairment: • Clobazam is extensively metabolized in the liver and consequently lower doses may be required

Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal and hepatic function, lower clobazam doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with clobazam is moderate Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • The risk category for clobazam has yet to be classified by the US Food and Drug Administration. However, it is likely to be in risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy] • Possible increased risk of birth defects when benzodiazepines are taken during pregnancy • Infants whose mothers received a benzodiazepine late in pregnancy may experience withdrawal effects • Neonatal flaccidity has been reported in infants whose mothers took a benzodiazepine during pregnancy • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • If drug is continued, start on folate 1 mg/day early in pregnancy to reduce risk of neural tube defects

Special populations

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

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• Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than clobazam monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of clobazam during pregnancy have not been identified Breast feeding • Breast milk:  clobazam plus N-desmethylclobazam:  13–36% of maternal plasma levels • Breastfed infants:  it is not known what plasma clobazam and N-desmethylclobazam concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects, including sedation and poor suckling • Recommend bottle feed particularly if infant shows signs of sedation

Clobazam

The overall place of clobazam in the treatment of epilepsy Clobazam should be tried as adjunctive medication in all drug-resistant epilepsies although it is less effective in symptomatic than in focal epilepsies. It is much less effective than clonazepam in myoclonic jerks and absences. Probably only 1 of 10 patients will have a clinically significant improvement, but this may be very dramatic and render the patient seizure-free. Clobazam has comparable effectiveness to carbamazepine and phenytoin as first-line monotherapy in children with newly diagnosed partial epilepsy. Primary seizure types: • All drug-resistant epilepsies Secondary seizure types: • Reading epilepsy • Febrile seizures • Catamenial epilepsy • Lennox-Gastaut syndrome • Startle epilepsy • Alcohol withdrawal seizures • Benign childhood partial epilepsies

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Potential advantages: • Although tolerance may develop, more than 30% of patients do not develop tolerance • When clobazam is effective, most patients continue to benefit for years without drug dependence or unwanted adverse effects

the epilepsy prescriber’s guide to antiepileptic drugs • Some patients (20%) experience dramatic seizure reduction and even become seizure-free

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Potential disadvantages: • Sedation • Development of tolerance • Associated with significant pharmacokinetic interactions and usually its metabolism is induced or inhibited • Potential teratogen, but not more than most other antiepileptic drugs

Clobazam, overall role

Suggested reading Anonymous. Clobazam has equivalent efficacy to carbamazepine and phenytoin as monotherapy for childhood epilepsy: Canadian Study Group for Childhood Epilepsy. Epilepsia 1998; 39: 952–959. Conry JA, Ng YT, Paolicchi JM, Kernitsky L, Mitchell WG, Ritter FJ, Collins SD, Tracy K, Kormany WN, Abdulnabi R, Riley B, Stolle J. Clobazam in the treatment of Lennox-Gastaut syndrome. Epilepsia 2009; 50: 1158–1166. Feely M, Gibson J. Intermittent clobazam for catamenial epilepsy:  tolerance avoided. Journal of Neurology, Neurosurgery, and Psychiatry 1984; 47: 1279–1282. Kinoshita M, Ikeda A, Begum T, Terada K, Shibashaki H. Efficacy of low-dose, add-on therapy of clobazam (CLB) is produced by its major metabolite, N-desmethyl-CLB. Journal of Neurological Sciences 2007; 263: 44–48. Mechndiratta MM, Krishnamurthy M, Rajesh KN, Singh G. Clobazam monotherapy in drug naïve adult patients with epilepsy. Seizure 2003; 12: 226–228. Ng YT, Collins SD. Clobazam. Neurotherapeutics 2007; 4: 138–144. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press, Guildford, UK; 2005. Riss J, Cloyd J, Gates J, Collins S. Benzodiazepines in epilepsy: pharmacology and pharmacokinetics. Acta Neurologica Scandinavica 2008; 118: 69–86. Sennoune S, Mesdjian E, Bonneton J, Genton P, Dravet C, Roger J. Interactions between clobazam and standard antiepileptic drugs in patients with epilepsy. Therapeutic Drug Monitoring 1992; 14: 269–274. Silva RC, Montenegro MA, Guerreiro CA, Guerreiro MM. Clobazam as add-on therapy in children with epileptic encephalopathy. Canadian Journal of Neurological Sciences 2006; 33: 209–213.

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Clonazepam Therapeutics Chemical name and structure: Clonazepam, 5-(2-chlorophenol)-1,3-dihydro-7-nitro-­2H-1,4 benzo­ diazepin-2-one, is a light yellow crystalline powder, with a molecular weight of 315.71 and an empirical formula of C15H10ClN3O3. H

O

N

NO2

N Cl

Clonazepam

Brand names: • Amotril; Antelepsin • Clonapilep; Clonatryl; Clonazepamum; Clonex; Clonopam; Clozer; Coquan • Iktorivil • Kenoket; Klonopin; Kriadex • Lansden; Lonazep • Neuryl • Paxam; Povanil • Ravotril; Riklona; Rivatril; Rivotril • Zepanc; Zymanta Generics available: • Yes Licensed indications for epilepsy: • Absence seizures (UK-SPC, FDA-PI) • Akinetic seizures (UK-SPC, FDA-PI) • Atonic seizures (UK-SPC) • Lennox-Gastaut syndrome (UK-SPC, FDA-PI) • Myoclonic seizures (UK-SPC, FDA-PI) • Status epilepticus (UK-SPC) Licensed indications for non-epilepsy conditions: • There are none

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Nonlicensed use for epilepsy: • Acquired epileptic aphasia (Landau-Kleffner syndrome)

the epilepsy prescriber’s guide to antiepileptic drugs • Infantile spasms (West syndrome) • Neonatal seizures

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Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Because of its sedation, problems during withdrawal, and hypersalivation, clonazepam is not indicated as first-line therapy for any type of seizures • Tonic status epilepticus can be worsened by clonazepam • Generalized tonic–clonic seizures can be exacerbated by clonazepam

Efficacy profile: • Clonazepam is commonly combined with other antiepileptic drugs for the treatment of seizures and usually only when bettertolerated adjunctive antiepileptic drugs have not been helpful • The goal of treatment is complete remission of seizures • Onset of action may occur within the first few days • Effective against partial and generalized seizures: especially absence and myoclonic seizures • Effective in the treatment of convulsive or nonconvulsive status epilepticus, although its use as a second-line drug has been superseded in many centers by diazepam, midazolam, and lorazepam • Continue treatment until all symptoms are gone or until improvement is stable and then continue treating indefinitely as long as improvement persists • Continue treatment indefinitely to avoid recurrence of seizures • If clonazepam is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome Pharmacokinetics Absorption and distribution: • Oral bioavailability: > 80% • Food co-ingestion:  it is not known whether food co-ingestion delays the rate of absorption or the extent of absorption • Tmax: 1–4 hours (adults); 2–3 hours (children) • Time to steady state: 2–10 days (adults); 5–7 days (children) • Pharmacokinetics: linear • Protein binding: 86%

Pharmacokinetics

Mechanism of action: • Binds to benzodiazepine receptors at the GABA A ligand-gated chloride channel complex • Enhances the inhibitory effects of GABA • Boosts chloride conductance through GABA-regulated channels

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the epilepsy prescriber’s guide to antiepileptic drugs

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• Volume of distribution: 1.5–4.4 L/kg • Salivary concentrations:  it is not known whether clonazepam is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma Metabolism: • Clonazepam is metabolized in the liver, primarily by CYP3A4, to 7-amino-clonazepam • 7-amino-clonazepam is in turn metabolized by acetylation, by means of N-acetyl-transferase, to form 7-acetamido-clonazepam • Clonazepam is also hydroxylated (isoenzymes not identified) to form 3-hydroxyclonazepam • The 7-amino-clonazepam metabolite retains some pharmacological activity; none of the other metabolites of clonazepam are pharmacologically active • Autoinduction is not a feature of clonazepam metabolism

Clonazepam

Elimination: • In healthy adult subjects half-life values are 17–56 hours • In adult patients with enzyme-inducing antiepileptic drugs halflife values are 12–46 hours • In children half-life values are 22–33 hours • In neonates half-life values are 22–81 hours • Renal excretion:  < 1% of an administered dose is excreted unchanged in urine Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on clonazepam: –– Carbamazepine, lamotrigine, phenobarbital, and phenytoin can increase the clearance of clonazepam and decrease clonazepam plasma levels • Interactions between AEDs: effects by clonazepam: –– To date, there have been no reports of clonazepam affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on clonazepam: –– Amiodarone and ritonavir can increase clonazepam plasma levels • Interactions between AEDs and non-AED drugs:  effects by clonazepam: –– To date, there have been no reports of clonazepam affecting the clearance of other non-AED drugs and affecting their plasma levels

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Pharmacodynamic drug interactions: • Clonazepam can potentiate the effects of CNS depressants such as alcohol, barbiturates, and neuroleptics

the epilepsy prescriber’s guide to antiepileptic drugs • In combination with valproate, clonazepam is associated with pharmacodynamic synergism in patients with absence seizures resulting in enhanced seizure control

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Hormonal contraception: • Clonazepam does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Common adverse effects: • Sedation, drowsiness, fatigue, depression • Dizziness, ataxia, slurred speech, nystagmus • Forgetfulness, confusion • Hyper-excitability, nervousness • Hypersalivation, dry mouth

Adverse effects

Adverse effects How drug causes adverse effects: • Same mechanism for adverse effects as for therapeutic effects  – namely due to excessive actions at benzodiazepine receptors • Long-term adaptations in benzodiazepine receptors may explain the development of dependence, tolerance, and withdrawal • Adverse effects are generally immediate, but immediate adverse effects often disappear in time

Life-threatening or dangerous adverse effects: • Withdrawal syndrome in chronic use • Respiratory depression, especially when taken with CNS depressants in overdose • Rare hepatic dysfunction, renal dysfunction, blood dyscrasias Rare and not life-threatening adverse effects: • Impotence • Loss of libido • Nausea, gastrointestinal symptoms • Pruritus • Urinary incontinence • Urticaria Weight change: • Not common; weight gain reported but not expected What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Lower the dose • Take largest dose at bedtime to avoid sedative effects during the day

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the epilepsy prescriber’s guide to antiepileptic drugs

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Dosing and use Usual dosage range: • Adults and children over 12 years of age: 4–10 mg/day • Children up to 12 years of age: 0.1–0.2 mg/kg/day Available formulations: • Tablets: 0.5 mg, 1 mg, 2 mg • Disintegrating wafer: 0.125 mg, 0.25 mg, 0.5 mg, 1 mg, 2 mg • Liquid formulation: 1 mg/mL for dilution before iv injection

Clonazepam

How to dose: • When initiating clonazepam treatment start with a low dose and titrate slowly so as to minimize adverse effects. –– For adults and children over 12 years of age:  start treatment with 0.25 mg/day at night and increase at weekly intervals in increments of 0.25 mg/day; maintenance dose generally 4–10 mg/day; at doses >4 mg/day some patients may require twice a day dosing. –– Children up to 12 years of age: start treatment with 0.01–0.02 mg/ day and slowly increase up to 0.1–0.2 mg/day –– Status epilepticus: the usual preparation for emergency treatment is a 1 mL ampule containing 1 mg clonazepam. For the treatment of early status epilepticus, clonazepam is usually given as a 1-mg iv bolus injection over 1 minute in adults, whereas 0.25–0.5 mg may be used in children. These doses can be repeated three times over a period of 3 hours. For established status epilepticus a short iv infusion may be used – clonazepam is constituted in a dextrose (5%) or 0.9% sodium chloride (normal saline) solution (1–2 mg in 250 mL) Dosing tips: • Doses much higher than 2 mg/day are associated with increased risk of dependence • Frequency of dosing in practice is often greater than predicted from half-life, as duration of biological activity is often shorter than the pharmacokinetic terminal half-life • Clonazepam accumulates during prolonged infusion, leading to hypotension, sedation, and finally, respiratory arrest. Too rapid an infusion may lead to severe hypotension and syncope, and continuous infusion should be avoided if possible

44

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as clonazepam is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Withdrawal should be undertaken with caution • Withdrawal at a rate of 0.25 mg per month will minimize withdrawal symptoms

the epilepsy prescriber’s guide to antiepileptic drugs • Typical withdrawal symptoms if withdrawal is abrupt include: rebound seizures, anxiety, tremor, insomnia, and, in some patients, psychotic episodes

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Overdose: • Rarely fatal in monotherapy: symptoms include sedation, confusion, coma, diminished reflexes • A fatality has been reported in a patient that overdosed with oxycodone and clonazepam • If indicated the stomach should be emptied by lavage or by induction of emesis • Treatment of overdose consists of supportive care and the administration of the benzodiazepine receptor antagonist flumazenil • Hemodialysis removes clonazepam from blood and, therefore, serves as a useful procedure in cases of overdose

Dosing and use

Tests and therapeutic drug monitoring: • During treatment:  periodic liver tests and blood counts may be prudent • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at clonazepam plasma concentrations of 0.013– 0.070 mg/L (0.041–0.222 μmol/L) –– The conversion factor from mg/L to μmol/L is 3.17 (i.e., 1 mg/L = 3.17 μmol/L) –– The reference range of clonazepam in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– There are no data indicating the usefulness of monitoring clonazepam by use of saliva Other warnings/precautions: • Use with caution in patients with pulmonary disease; rare reports of death after initiation of benzodiazepines in patients with severe pulmonary impairment • Use only with extreme caution if patient has obstructive sleep apnea • Some depressed patients may experience a worsening of suicidal ideation • Some patients may exhibit abnormal thinking or behavioral changes similar to those caused by other CNS depressants (i.e., either depressant actions or disinhibiting actions) • Clonazepam is a Schedule IV drug and the risk of dependence may increase with dose and duration of treatment Do not use: • If patient has respiratory depression • If patient has acute pulmonary insufficiency

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• If patient has sleep apnea syndrome • If patient has marked neuromuscular respiratory weakness, including unstable myasthenia gravis • If patient has severe liver disease • If there is a proven allergy to clonazepam or any other benzodiazepine

Special populations Renal impairment: • Clonazepam is renally secreted, so the dose may need to be lowered • Because clonazepam can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of clonazepam Hepatic impairment: • Clonazepam is extensively metabolized in the liver and consequently lower doses may be required

Clonazepam

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Long-term effects of clonazepam on children/adolescents are unknown • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal and hepatic function, lower clonazepam doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with clonazepam is moderate

46

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Clonazepam is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy]

the epilepsy prescriber’s guide to antiepileptic drugs • Possible increased risk of birth defects when benzodiazepines are taken during pregnancy • Infants whose mothers received a benzodiazepine late in pregnancy may experience withdrawal effects • Neonatal flaccidity has been reported in infants whose mothers took a benzodiazepine during pregnancy • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetics of clonazepam during pregnancy have not been identified

The overall place of clonazepam in the treatment of epilepsy Clonazepam, primarily as adjunctive therapy but also as monotherapy, is the most effective antiepileptic drug in the treatment of myoclonic jerks (superior to valproate), and is also effective in absences (although not as effective as valproate and ethosuximide). It is probably the drug of choice for reading epilepsy (superior to valproate) and is particularly effective in juvenile myoclonic epilepsy if the myoclonic jerks are not controlled by other antiepileptic drugs. It has proven efficacy in tonic–clonic, partial and absence status.

Clonazepam, overall role

Breast feeding • Breast milk: 13–33% of maternal plasma levels • Breastfed infants: it is not known what plasma clonazepam concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects, including sedation and apnea • If adverse effects are observed recommend bottle feed

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Primary seizure types: • Myoclonic jerks • Absences • Juvenile myoclonic epilepsy • Status epilepticus • Reading epilepsy Secondary seizure types: • Acquired epileptic aphasia (Landau-Kleffner syndrome) • Infantile spasms (West syndrome) • Neonatal seizures Potential advantages: • Can be used as an adjunct or as monotherapy • Generally used as second-line treatment for absence seizures if valproate or ethosuximide are ineffective

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Clonazepam 48

• Rapid onset of action • Less sedation than some other benzodiazepines • Longer duration of action than some other benzodiazepines (e.g., diazepam and midazolam) • Availability of oral disintegrating wafer • Easier to taper than some other benzodiazepines because of long half-life • May have less abuse potential than some other benzodiazepines • May cause less depression, euphoria, or dependence than some other benzodiazepines Potential disadvantages: • Development of tolerance may require dose increases • Risk of dependence and/or tolerance, particularly for treatment periods longer than 12 weeks • Potential for accumulation on prolonged infusion • Respiratory arrest, hypotension, sedation and thrombophlebitis • Associated with significant pharmacokinetic interactions and usually its metabolism is induced or inhibited • Potential teratogen, but not more than most other antiepileptic drugs Suggested reading Dreifuss FE, Penry JK, Rose SW, Kupferberg HJ, Dyken P, Sato S. Serum clonazepam concentrations in children with absence seizures. Neurology 1975; 23: 255–258. Greenblatt DJ, Miller LG, Shader RI. Clonazepam pharmacokinetics, brain uptake, and receptor interactions. Journal of Clinical Psychiatry 1987; 48(Suppl): 4–11. Hakeem VF, Wallace SJ. EEG monitoring of therapy for neo­ natal seizures. Developmental Medicine and Child Neurology 1990; 32: 858–864. Mireles R, Leppik IL. Valproate and clonazepam comedication in patients with intractable epilepsy. Epilepsia 1985; 26: 122–126. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press, Guildford, UK; 2005. Sironi VA, Miserocchi G, DeRiu PL. Clonazepam withdrawal syndrome. Acta Neurologica 1984; 6: 134–139.

the epilepsy prescriber’s guide to antiepileptic drugs

Diazepam Therapeutics Chemical name and structure: Diazepam, 7-chloro-1,3-dihydro-1-methyl-5-phenyl-2H-1,4 benzo­ diazepin-2-one, is a yellowish crystalline powder, with a molecular weight of 284.7 and an empirical formula of C16H13ClN2O. H 3C

D

O N

Cl

N

therapeutics

Brand names: • Aliseum; Anlin; Ansiolin; Antenex; Apaurin; Apo-diazepam; Apozepam; Assival; Azepan • Benzopin • Calmpose; Cercine; Ceregulart; Compaz; Condition • D-Pam; Dialag; Diano; Diapam; Diapin; Diapine; Diapo; Diastat; Diaz; Diazem; Diazemuls; Diazepam; Diazepam Desitin; Diazepam RecTubes; Diazepam-Eurogenerics; Diazepam-Lipuro; Diazepamratiopharm; Diazepan; Diazer; Diazerekt; Dipaz; Dipezona; Doval; Ducene; Dupin; DZP • Elcion CR; Euphorin; Gewacalm • Horizon • Ifa Fonal • Kratium; Kratium 2 • Lembrol • Melode • Nivalen; Nixtensyn; Noan; Normabel • Ortopsique (MX) • Paceum; Pacitran; Pax; Paxum; Placidox; Plidan; Propam; Psychopax • Rectubes; Radizepam; Relanium; Relsed; Renborin • Seduxen; Serenzin; Sipam; Stesolid; Stesolid Rectal Tube; Sunzepam • Tranquirit • Valaxona; Valdimex; Valiquid; Valisanbe; Valium; Valiuzam; Valpam; Vanconin; Vatran; Volclair

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the epilepsy prescriber’s guide to antiepileptic drugs

D

Generics available: • Yes Licensed indications for epilepsy: • Status epilepticus: injection only (UK-SPC; FDA-PI) • Febrile convulsions (UK-SPC) • Bouts of increased seizure activity (acute repetitive seizures) (FDA-PI) Licensed indications for non-epilepsy conditions: • Anxiolytic (UK-SPC; FDA-PI) • Skeletal muscle relaxant (UK-SPC; FDA-PI) • Peri-operative sedative and analgesic (UK-SPC; FDA-PI) Nonlicensed use for epilepsy: • There are none

Diazepam

Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Can induce status epilepticus in patients with Lennox-Gastaut syndrome • Should not be used as a long-term antiepileptic drug Mechanism of action: • Binds to benzodiazepine receptors at the GABA-A ligand-gated chloride channel complex • Boosts chloride conductance through GABA-regulated channels Efficacy profile: • Diazepam is the most widely used benzodiazepine in epilepsy • It is the drug of first choice for the treatment of the premonitory stages of status epilepticus, for early status epilepticus, for serial seizures, for prolonged seizures, and for the prophylaxis of serial seizures

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: 100% • Tmax:  30–90 minutes (tablets); 10–60 minutes (rectal solution); 30–60 minutes (rectal gel) • Time to steady state:  6–11 days (diazepam); 15–20 days (N-desmethyldiazepam)  – applies to adults on nonenzyme­inducing antiepileptic drugs

the epilepsy prescriber’s guide to antiepileptic drugs • Pharmacokinetics: linear, but accumulation occurs following repeat administration • Protein binding: 97–99% • Volume of distribution: 1.1 L/kg • Salivary concentrations: it is not known whether diazepam is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

Elimination: • Plasma concentrations decline rapidly with an initial half-life of ~1 hour • In healthy adult subjects half-life values for diazepam are 28–54 hours, whereas for N-desmethyldiazepam values are 72–96 hours • In adult patients with enzyme-inducing antiepileptic drugs halflife values for diazepam are 31–41 hours • In children half-life values are 14–20 hours • In neonates half-life values are 29–33 hours • In the elderly half-life values for diazepam are 80–100 hours, whereas for N-desmethyldiazepam values are 91–211 hours • In patients with hepatic insufficiency half-life values for diazepam are 59–116 hours, whereas for N-desmethyldiazepam values are 68–148 hours • Renal excretion: < 5% of an administered dose is excreted unchanged in urine

Pharmacokinetics

Metabolism: • Diazepam is metabolized by desmethylation in the liver to desmethyldiazepam primarily by CYP2C19 but CYP3A4 also contributes • N-desmethyldiazepam is in turn metabolized by hydroxylation, by means of CYP2C19, to form oxazepam which is either excreted unchanged or undergoes sequential metabolism to a glucuronide conjugate • Diazepam is also hydroxylated, by CYP3A4, to form temaze­ pam which in turn is demethylated to oxazepam or excreted unchanged • N-desmethyldiazepam, along with the oxazepam and temazepam metabolites are pharmacologically active • N-desmethyldiazepam accumulates in blood to concentrations 7-fold higher than diazepam and contributes significantly to the pharmacological effect of diazepam • A complication of diazepam metabolism is that it undergoes enterohepatic circulation, which can result in increased plasma levels and recurrence of drowsiness after 6–8 hours due to absorption from the gastrointestinal tract after excretion in the bile • Autoinduction is not a feature of diazepam metabolism

D

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the epilepsy prescriber’s guide to antiepileptic drugs

D

Diazepam

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on diazepam: –– Carbamazepine, phenytoin, phenobarbital, and primidone can increase the clearance of diazepam and N-desmethyldiazepam and decrease diazepam and N-desmethyldiazepam plasma levels –– Valproic acid can displace diazepam from its plasma protein binding sites and also inhibit its metabolism so that unbound diazepam levels are increased whereas N-desmethyldiazepam levels are decreased • Interactions between AEDs: effects by diazepam: –– To date, there have been no reports of diazepam affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on diazepam: –– Cimetidine, disulfiram and omeprazole can increase diazepam plasma levels • Interactions between AEDs and non-AED drugs:  effects by diazepam: –– To date, there have been no reports of diazepam affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • Diazepam depressive effects may be increased when taken with other CNS depressants Hormonal contraception: • Diazepam does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects How drug causes adverse effects: • Same mechanism for adverse effects as for therapeutic effects  – namely due to excessive actions at benzodiazepine receptors • Long-term adaptations in benzodiazepine receptors may explain the development of dependence, tolerance, and withdrawal • Adverse effects are generally immediate, but immediate adverse effects often disappear in time

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Common adverse effects: • Sedation, fatigue, depression • Dizziness, ataxia, slurred speech, weakness • Forgetfulness, confusion • Hyper-excitability, nervousness • Hypersalivation, dry mouth • Pain at injection site, phlebitis, venous thrombosis

the epilepsy prescriber’s guide to antiepileptic drugs Life-threatening or dangerous adverse effects: • Respiratory depression, especially when taken with CNS depressants in overdose • Rare hepatic dysfunction, renal dysfunction, blood dyscrasias • Rare hypotension

D

Rare and not life-threatening adverse effects: • Jaundice • Urinary retention, incontinence • Libido reduced, gynecomastia Weight change: • Not common; weight gain reported but not expected

Dosing and use Usual dosage range • In status epilepticus: –– iv bolus (undiluted) 10–20 mg – adults; 0.2–0.3 mg/kg – child­ ren; rate not to exceed 2–5 mg/min and this can be repeated –– rectal administration 10–30 mg  – adults; 0.5–0.75 mg/kg  – ­children; this can be repeated after 15 minutes if necessary

Dosing and use

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Lower the dose

Available formulations: • Tablets: 2 mg, 5 mg, 10 mg • Liquid solution for injection: 5 mg/5 mL • Liquid emulsion for injection: 5 mg/5 mL • Rectal tubes (solution): 2.5 mg/1.25 mL, 5 mg/2.5 mL, 10 mg/ 2.5 mL • Rectal suppositories: 10 mg • Rectal gel (5 mg/mL): 2.5 mg, 5 mg, 10 mg, 15 mg, 20 mg How to dose: Solutions need to be freshly prepared because diazepam is absorbed by polyvinylchloride plastics; typically fresh solutions should be made up within 6 hours • Infusions should be carefully mixed so that 20 mg (Valium) should not be dissolved in less than 250 mL of solvent (4% dextrose, 0.18% sodium chloride) as there is a danger of precipitation at higher concentrations

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the epilepsy prescriber’s guide to antiepileptic drugs

D

• Diazemuls can be diluted in 5% or 10% dextrose solution to a maximum concentration of 200 mg in 500 mL and Stesolid to a maximum 10 mg in 200 mL of dextrose-saline • Liquid formulation should be mixed with water or fruit juice, applesauce, or pudding • Because of risk of respiratory depression, rectal diazepam treatment should not be given more than once in 5 days or more than twice during treatment course, especially for alcohol withdrawal or status epilepticus

Diazepam

Dosing tips: • Only benzodiazepine with a formulation specifically for rectal administration • One of the few benzodiazepines available in an oral liquid formula­ tion • One of the few benzodiazepines available in an injectable formula­ tion • Diazepam injection is intended for acute use; patients who require long-term treatment should be switched to the oral formulation • Diazepam is a Schedule IV drug and the risk of dependence may increase with dose and duration of treatment How to withdraw drug: • There is no need to adjust dosage of concurrent medications as diazepam is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Patients with a history of seizures may seize upon withdrawal, especially if withdrawal is abrupt • Taper by 2 mg every 3 days to reduce chances of withdrawal effects • For difficult to taper cases, consider reducing dose much more slowly after reaching 20 mg/day, perhaps by as little as 0.5–1 mg every week or less Overdose: • Fatalities can occur: symptoms include hypotension, tiredness, ataxia, confusion, coma • The stomach should be emptied immediately by lavage or by induction of emesis • Treatment of overdose consists of supportive care and the administration of the benzodiazepine receptor antagonist flumazenil • Hemodialysis does not removes diazepam from blood and, therefore, is not a useful procedure in cases of overdose

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Tests and therapeutic drug monitoring: • During treatment:  periodic liver tests and blood counts may be prudent • Therapeutic drug monitoring: –– Diazepam plasma levels are not routinely used to guide patient management

the epilepsy prescriber’s guide to antiepileptic drugs

Other warnings/precautions: • Use with caution in patients with pulmonary disease; rare reports of death after initiation of benzodiazepines in patients with severe pulmonary impairment • Some depressed patients may experience a worsening of suicidal ideation • Some patients may exhibit abnormal thinking or behavioral changes similar to those caused by other CNS depressants (i.e., either depressant actions or disinhibiting actions)

D

special populations

–– The minimum plasma level required to suppress seizures probably depends on seizure type, duration of therapy and other clinical factors but ranges from 200–600 ng/mL (702–2106 nmol/L) in most emergency settings –– For initial seizure control plasma levels of 550 ng/mL (1930 nmol/L) are suggested –– For maintenance of seizure control plasma levels of 150–300 ng/ mL (526–1053 nmol/L) are suggested –– The conversion factor from ng/mL to nmol/L is 3.17 (i.e., 1 ng/ mL = 3.51 nmol/L) –– The reference ranges highlighted above are considered to be the same for children and adults although no data are available to support this clinical practice –– There are no data indicating the usefulness of monitoring diazepam by use of saliva

Do not use: • If patient has respiratory depression • If patient has acute pulmonary insufficiency • If patient has sleep apnea syndrome • If patient has marked neuromuscular respiratory weakness, including unstable myasthenia gravis • If patient has severe liver disease • If there is a proven allergy to diazepam or any other benzo­ diazepine

Special populations Renal impairment: • Diazepam is renally secreted, so the dose may need to be lowered Hepatic impairment: • Diazepam is extensively metabolized in the liver and consequently lower doses may be required • Initial dose is 2–2.5 mg, one–two times/day; increase gradually as needed

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the epilepsy prescriber’s guide to antiepileptic drugs

D

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Neonates and infants have deceased hydroxylation and glucuronidation capacity which may result in a decreased clearance of diazepam • 6 months and up: initial 1–2.5 mg, three–four times/day; increase gradually as needed • Parenteral administration should only be undertaken in children 30 days or older • Rectal administration should only be undertaken in children 2 years or older • Long-term effects of diazepam in children/adolescents are unknown; should generally receive lower doses and be more closely monitored

Diazepam

Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal and hepatic function, lower diazepam doses are appropriate • Initial 2–2.5 mg, one–two times/day; increase gradually as needed Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Diazepam is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy] • Possible increased risk of birth defects when benzodiazepines taken during pregnancy • Infants whose mothers received a benzodiazepine late in pregnancy may experience withdrawal effects • Neonatal flaccidity has been reported in infants whose mothers took a benzodiazepine during pregnancy • Seizures, even mild seizures, may cause harm to the embryo/fetus

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Breast feeding • Breast milk: some drug is found in mother’s breast milk • Breastfed infants: it is not known what plasma diazepam concentrations are achieved in breastfed infants compared with the levels of their mothers

the epilepsy prescriber’s guide to antiepileptic drugs • Recommend either to discontinue drug or bottle feed • Effects on infant have been observed and include feeding difficulties, sedation, and weight loss

Primary seizure types: • Status epilepticus Secondary seizure types: • None Potential advantages: • Ease of administration by means of intravenous bolus injection or by rectal route in the premonitory stage • Rapid onset of action • Multiple dosage formulations (oral, tablet, oral liquid, rectal gel, injectable) allow more flexibility in administration compared with most other benzodiazepines

Diazepam, overall role

The overall place of diazepam in the treatment of epilepsy Diazepam is a widely used benzodiazepine in epilepsy treatment. It is the drug of choice in the management of premonitory or early stages of status epilepticus and is effective in a wide range of established status types.

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Potential disadvantages: • Accumulates on repeated administration, with risk of sudden respiratory depression, sedation, and hypotension • Short duration of action, tendency to relapse following single injection • Rectal suppositories should not be used because absorption is too slow • Pharmacologically active metabolite (N-desmethyldiazepam) which accumulates at concentrations many-fold higher than that of diazepam • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Agurell S, Berlin A, Ferngren H, Hellstrom B. Plasma levels of diazepam after parenteral and rectal administration. Epilepsia 1975; 16: 277–283. Dhillon S, Richens A. Valproic acid and diazepam interaction in vivo. British Journal of Clinical Pharmacology 1982; 13: 553–560. Klotz U, Antonin KH, Brugel H, Bieck JR. Disposition of diazepam and its major metabolite desmethyldiazepam in patients with

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Diazepam 58

liver disease. Clinical Pharmacology and Therapeutics 1977; 21: 430–436. Meberg A, Langslet A, Bredesen JE, Lunde PKM. Plasma concentration of diazepam and N-desmethyldiazepam in children after a single rectal or intramuscular dose. European Journal of Clinical Pharmacology 1978; 12: 273–276. Norris E, Marzouk O, Nunn A, McIntyre J, Choonari I. Respiratory depression in children receiving diazepam for acute seizures: a prospective study. Developmental Medicine and Neurology 1999; 41: 340–343. Prensky AL, Raff MC, Moore MS, Schwab RS. Intravenous diazepam in the treatment of prolonged seizure activity. New England Journal of Medicine 1967; 276: 779–886. Schwartz MA, Koechlin BA, Postma E, Palmer S, Krol G. Metabolism of diazepam in rat, dog and man. Journal of Pharmacology and Experimental Therapeutics 1965; 149: 423–435. Shorvon S. Status epilepticus: its clinical features and treatment in children and adults. Cambridge University Press: Cambridge; 1994.

the epilepsy prescriber’s guide to antiepileptic drugs

Eslicarbazepine Acetate Therapeutics Chemical name and structure: Eslicarbazepine acetate, (S)-10-acetoxy-10,11-dihydro-5H-dibenz[b,f ] azepine-5-carboxamide, is a white to off-white crystalline powder, with a molecular weight of 296.32 and an empirical formula of C17H16N2O3. H3C

E

O O

C NH2

therapeutics

N O

Brand names: • Exalief • Stedesa • Zebinix Generics available: • No Licensed indications for epilepsy: • Adjunctive treatment of partial onset seizures with or without secondary generalization in patients with epilepsy aged 16 years and older (UK-SPC) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • The efficacy of eslicarbazepine acetate in primary generalized seizures has not been determined and therefore its use is not recommended in these patients

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the epilepsy prescriber’s guide to antiepileptic drugs

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Mechanism of action: • Acts as a use-dependent blocker of voltage-sensitive sodium channels resulting in stabilization of hyperexcitable neuronal membranes • An effect on glutamate release may also occur

Eslicarbazepine Acetate

Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 4 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If eslicarbazepine acetate is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Pharmacokinetics Absorption and distribution (all values refer to eslicarbazepine): • Oral bioavailability: >90% • Food co-ingestion: neither delays the rate of absorption nor decreases the extent of absorption • Tmax: 2–3 hours • Time to steady state: 4–5 days • Pharmacokinetics: linear • Protein binding: 30%; blood cell bound fraction: 46% • Volume of distribution: 2.7 L/kg • Salivary concentrations: it is not known whether eslicarbazepine is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma Metabolism: • Eslicarbazepine acetate is rapidly metabolized (hydrolysis) in the liver to its pharmacologically active metabolite, eslicarbazepine (also known as S-licarbazepine), by esterases (91%) • Other minor metabolites, which are pharmacologically active, include R-licarbazepine (~5%) and oxcarbazepine (~1%) • Eslicarbazepine (33%) is subsequently metabolized by conjugation with glucuronic acid • Although the metabolites of eslicarbazepine are pharmacologically active, they contribute to <5% of activity • Autoinduction is not a feature of eslicarbazepine acetate metabolism

60

Elimination: • Half-life of eslicarbazepine acetate is <2 hours; thus eslicarbaze­ pine acetate is a prodrug rapidly converted to its eslicarbazepine metabolite • In the absence of enzyme-inducing AEDs, half-life values for eslicarbazepine are 20–24 hours

the epilepsy prescriber’s guide to antiepileptic drugs • In the presence of enzyme-inducing AEDs, half-life values for eslicarbazepine are 13–20 hours • Renal excretion: 92% of an administered dose is excreted as eslicarbazepine metabolites in urine; 33% as a glucuronide conjugate of eslicarbazepine and 67% as unchanged eslicarbazepine; 8% of metabolites comprise (R)-licarbazepine and oxcarbazepine and glucuronide conjugates of eslicarbazepine acetate, eslicarbazepine, (R)-licarbazepine, and oxcarbazepine • Renal excretion: <1% of an administered dose is excreted unchanged as eslicarbazepine acetate in urine

adverse effects

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs – effects on eslicarbazepine: –– Carbamazepine and phenytoin can increase the clearance of eslicarbazepine and decrease eslicarbazepine plasma levels • Interactions between AEDs – effects by eslicarbazepine: –– Eslicarbazepine can increase plasma levels of phenytoin –– Eslicarbazepine can decrease plasma levels of lamotrigine and topiramate • Interactions between AEDs and non-AED drugs  – effects on eslicarbazepine: –– To date there have been no reports of other non-AED drugs affecting the clearance of eslicarbazepine and affecting eslicarbazepine plasma levels • Interactions between AEDs and non-AED drugs  – effects by eslicarbazepine: –– Eslicarbazepine can decrease plasma levels of warfarin

E

Pharmacodynamic drug interactions: • Concurrent treatment with carbamazepine can be associated with a greater incidence of diplopia, abnormal coordination, and dizziness Hormonal contraception: • Eslicarbazepine acetate enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking eslicarbazepine acetate

Adverse effects How drug causes adverse effects: • CNS adverse effects may be due to excessive actions at voltagesensitive sodium channels

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the epilepsy prescriber’s guide to antiepileptic drugs

E

Common adverse effects: • Dizziness, headache, abnormal coordination, somnolence, tremor, disturbance in attention • Diplopia, blurred vision • Vertigo • Nausea, vomiting, diarrhea • Rash • Fatigue, gait disturbance

Eslicarbazepine Acetate

Life-threatening or dangerous adverse effects: • Increases PR interval therefore patients with known second- or third-degree atrioventricular block may be at risk of myocardial infarction or heart failure • Particular caution should be exercised with the elderly as they may be at an increased risk of cardiac disorders and prescribed Class I antiarrhythmic drugs and also may be co-prescribed antiepileptic drugs (e.g., carbamazepine, lacosamide, lamotrigine, and pregabalin) that are known to be associated with PR prolongation • Increased risk of suicidal ideation and behavior • Rare adverse reactions, including Stevens-Johnson syndrome, bone marrow depression, serious cardiac arrhythmias, or systemic lupus erythematosus have not been observed but as they can be a feature of oxcarbazepine treatment, caution needs to be exercised with eslicarbazepine acetate Rare and not life-threatening adverse effects: • Constipation • Nasopharyngitis Weight change: • Not common What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Risk of adverse effects is greatest in the first few months of treatment • Common adverse effects such as nausea often abate after a few months Dosing and use Usual dosage range: • Adults: 800–1200 mg/day

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Available formulations: • Tablets: 400 mg, 800 mg • Suspension: 60 mg/mL

the epilepsy prescriber’s guide to antiepileptic drugs How to dose: • When initiating eslicarbazepine acetate treatment start with a low dose and titrate slowly so as to minimize adverse effects –– For adults of age 16 years or older: start treatment with 400 mg once daily for 1–2 weeks; increase by 400 mg/day at bi-weekly intervals; maximum dose 1200 mg/day, given once daily

E

Dosing tips: • Titration of dose should be undertaken based on individual tolerability and response to the drug • Concomitant use with oxcarbazepine should be avoided because it may result in overexposure to the pharmacologically active metabolites of both drugs

Dosing and use

How to withdraw drug: • May need to adjust dosage of concurrent medications as eslicarbazepine acetate is being discontinued, since plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper:  a gradual dose reduction over a minimum of a 1-week period should be undertaken • Rapid discontinuation may increase the risk of seizures Overdose: • Following accidental overdose vertigo, walking instability, and hemiparesis has occurred • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes eslicarbazepine and its metabolites from blood and therefore may be a useful procedure in case of overdose; two dialysis sessions may be necessary to virtually eliminate eslicarbazepine and its metabolites Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests • During treatment: liver and kidney function tests every 12 months • Therapeutic drug monitoring: –– There are no data relating the plasma concentration of eslicarbazepine with that of seizure suppression –– Thus, although routine monitoring of eslicarbazepine is not ­recommended, measurement of plasma eslicarbazepine concentrations may be useful as a check on compliance –– There are no data indicating the usefulness of monitoring eslicarbazepine by use of saliva Other warnings/precautions: • Use cautiously in patients who have demonstrated hypersensitivity to carbamazepine and/or oxcarbazepine

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Eslicarbazepine Acetate

• Eslicarbazepine acetate can cause dizziness and somnolence which could increase the occurrence of accidental injury or falls • Because eslicarbazepine acetate has a tricyclic chemical structure, it is not recommended to be taken with MAOIs • In patients with pre-existing renal conditions associated with low sodium or in patients treated with sodium-lowering medications (e.g. diuretics, desmopressin, non-steroidal anti-inflammatory drugs [e.g., indometacin]) blood sodium levels should be measured prior to initiating treatment with eslicarbazepine acetate; thereafter, sodium levels should be measured after ~2 weeks and then at monthly intervals for the first 3 months or according to clinical need • Usually hyponatremia (sodium levels <125 mmol/L) is asymptomatic and dose adjustment is not necessary; however if it becomes clinically significant (typically occurs in <1% of patients), it can be reversed by either restricting fluid intake or a reduction in eslicarbazepine acetate dose Do not use: • If patient has a proven allergy to eslicarbazepine acetate or to any of the excipients • Hypersensitivity to other carboxamide derivatives (e.g. carbamazepine and oxcarbazepine) • If patient is taking an MAOI • If patient has conduction problems or severe cardiac disease such as a history of myocardial infarction or heart failure

Special populations Renal impairment: • Eslicarbazepine and its metabolites are renally excreted • Mild to moderate renal impairment (CrCL >30 – <60 mL/min) results in a 40–80% decrease in clearance; an initial dose of 400 mg every other day for 2 weeks followed by a once daily dose of 400 mg is recommended • Severe renal impairment (CrCL <30 mL/min) results in a 90% decrease in clearance; eslicarbazepine acetate is not recommended for these patients • Because eslicarbazepine can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of eslicarbazepine acetate

64

Hepatic impairment: • Eslicarbazepine acetate undergoes significant first pass metabolism (91%) in the liver, and in patients with moderate hepatic impairment (Child-Pugh B) a slight increase in eslicarbazepine plasma levels occurs but a dose adjustment is not considered necessary

the epilepsy prescriber’s guide to antiepileptic drugs Children: • Eslicarbazepine acetate is not licensed for use in children • Nevertheless, preliminary data show that for children, all of which have an increased metabolic capacity, higher doses on a mg/kg basis are required in order to achieve the equivalent therapeutic plasma levels seen in adults • Children may benefit from twice daily dosing • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Eslicarbazepine acetate has yet to be classified by the US Food and Drug Administration; when classified it will probably be in risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than eslicarbazepine acetate monotherapy • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of eslicarbazepine during pregnancy are not available

Special populations

Elderly: • Elderly patients are more susceptible to adverse effects and therefore tolerate lower doses better • Because of an age-related reduction in renal function, lower eslicarbazepine acetate doses are appropriate • Because eslicarbazepine acetate is associated with dizziness and somnolence the elderly are at increased risk of accidental injury (fall) • The elderly with pre-existing renal conditions, and who may be taking sodium-lowering medications or non-steroidal anti­inflammatory drugs, have an increased risk of developing symptomatic hyponatremia • Invariably the elderly are prescribed drug therapies for concurrent comorbidities; however, the risk of pharmacokinetic interactions with eslicarbazepine acetate is minimal

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the epilepsy prescriber’s guide to antiepileptic drugs

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Breast feeding • Breast milk:  it is not known whether eslicarbazepine acetate or eslicarbazepine are excreted in breast milk • Breastfed infants  – It is not known what plasma eslicarbazepine acetate or eslicarbazepine concentrations are achieved in breastfed infants compared to the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

Eslicarbazepine Acetate

The overall place of eslicarbazepine acetate in the treatment of epilepsy Eslicarbazepine acetate is the latest antiepileptic drug to be licensed for clinical use (2009). It is structurally related to carbamazepine and oxcarbazepine and is licensed for use as adjunctive treatment of partial-onset seizure (with or without secondary generalization) in patients with epilepsy aged 16 years and older. Because of its recent introduction, it is too early to ascertain the place of eslicarbazepine acetate in the treatment of patients with epilepsy Primary seizure types: • Partial seizures with or without secondary generalization Secondary seizure types: • None Potential advantages: • Its structural similarity to carbamazepine and oxcarbazepine results in an antiepileptic drug with a well-validated mode of action • Not associated with the problematic pharmacologically active metabolite (carbamazepine-10,11-epoxide) that occurs with carbamazepine • Dosing schedule is once per day Potential disadvantages: • Particular caution is warranted when prescribed with carbamazepine or oxcarbazepine as adverse effects associated with the latter drugs may be exacerbated • In Europe only an 800 mg tablet formulation has been licensed and thus tablet cutting will be needed so as to achieve the recommended clinically effective dose range • Potential teratogen, but not more than most other antiepileptic drugs

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Suggested reading Almeida L, Soares-da-Silva P. Eslicarbazepine acetate (BIA- 2–093). Neurotherapeutics 2007; 4: 88–96. Almeida L, Falcao A, Maia J, Mazur D, Gellert M, Soares-da-Silva P. Single-dose and steady-state pharmacokinetics of eslicarbazepine

the epilepsy prescriber’s guide to antiepileptic drugs

E Eslicarbazepine Acetate, overall role

acetate (BIA 2–093) in healthy elderly and young subjects. Journal of Clinical Pharmacology 2005; 45: 1062–1066. Almeida L, Potgieter JH, Maia J, Potgieter MA, Moto F, Soares-daSilva P. Pharmacokinetics of eslicarbazepine acetate in patients with moderate hepatic impairment. European Journal of Clinical Pharmacology 2008; 64: 267–273. Bonifacio MJ, Sheridan RD, Parada A, Cunha RA, Patmore L, Soares-da-Silva P. Interaction of the novel anticonvulsant, BIA 2–093, with voltage-gated sodium channels:  Comparison with carbamazepine. Epilepsia 2001; 42: 600–608. Elger C, Halasz P, Maia J, Almeida L, Soares-da-Silva P, on behalf of the BIA-2093–301 Investigators Study Group. Efficacy and safety of eslicarbazepine acetate as adjunctive treatment in adults with refractory partial-onset seizures:  A randomized, double-blind, placebo controlled, parallel-group phase III study. Epilepsia 2009; 50: 454–463. Gil-Nagel A, Lopes-Lima J, Almeida L, Maia J, Soares-da-Silva P, on behalf of the BIA-2093–303 Investigators Study Group. Efficacy and safety of 800 and 1200 mg eslicarbazepine acetate as adjunctive treatment in adults with refractory partial-onset seizures. Acta Neurologica Scandinavica 2009; 120: 281–287. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. Meis J, Almeida L, Falcao A, Soares E, Mota F, Potgieter MA, Potgieter JH, Soares-da-Silva P. Effect of renal impairment on the pharmacokinetics of eslicarbazepine acetate. International Journal of Clinical Pharmacology and Therapeutics 2008; 463: 119–130. Meis J, Vaz-de-Silva M, Almeida L, Falcao A, Silveira P, Guimaraes S, Graziela P, Soares-da-Silva P. Effect of food on the pharmacokinetic profile of eslicarbazepine (BIA 2–093). Drugs R D 2005; 64: 201–206.

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Ethosuximide Therapeutics Chemical name and structure: Ethosuximide, 2-ethyl-2-methylsuccinimide, is a white crystalline powder, with a molecular weight of 141.7 and an empirical formula of C7H11NO2 . O

H N O

Ethosuximide

Brand names: • Asamid • Emeside; Ethymal; Etomal; Etosuximida • Fluozoid • Petimid; Petinimid; Petnidan • Ronton • Suxilep; Suximal; Suxinutin • Zarondan; Zarontin Generics available: • Yes Licensed indications for epilepsy: • As monotherapy for absence seizures (UK-SPC) • Control of absence (petit mal) epilepsy (FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • Atypical absence seizures • Myoclonic seizures • Astatic seizures (drop attacks) Nonlicensed use for non-epilepsy conditions: • There are none

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Ineffective (contraindicated): • Generalized tonic–clonic seizures • Partial onset seizures

the epilepsy prescriber’s guide to antiepileptic drugs Mechanism of action: • No single unifying mechanism of action of ethosuximide has been identified • The prevailing hypothesis is that thalamic low-threshold calcium channels (T for “transient” or “tiny” channels) are involved. It has been demonstrated that ethosuximide, at therapeutic concentrations, can either reduce the number or reduce the conductance of these channels • Ethosuximide also inhibits so-called noninactivating sodium currents and calcium-dependent potassium channels, but not lowthreshold calcium channels of thalamocortical neurons

Pharmacokinetics

Efficacy profile: • Goal of therapy in typical absence seizures is not only full seizure control, but also normalization of EEG • Onset of action may occur within the first few days • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • Myoclonic seizures associated with various epileptic syndromes, such as Lennox-Gastaut syndrome, severe myoclonic epilepsy of infancy, juvenile myoclonic epilepsy, and myoclonic astatic epilepsy, may also at times respond to ethosuximide • If partially effective, consider co-prescribing with lamotrigine or valproic acid, or switch to valproic acid, lamotrigine, levetiracetam, acetazolamide, topiramate, or zonisamide

E

Pharmacokinetics Absorption and distribution: • Oral bioavailability: >90%, both for capsules and liquid formulations • Food co-ingestion:  it is not known whether food co-ingestion delays the rate of absorption or decreases the extent of absorption • Tmax: ~1–4 hours, slightly longer for capsules than for syrup • Time to steady state: 8–12 days (adults); 6–8 days (children) • Volume of distribution: 0.7 L/kg (for all age groups) • Pharmacokinetics: linear • Protein binding: 0% • Salivary concentrations:  ethosuximide is secreted into saliva and concentrations are similar to the unbound levels seen in plasma Metabolism: • Ethosuximide is metabolized in the liver by hydroxylation to form isomers of 2-(1-hydroxyethyl)-2-methylsuccinimide, of which at least 40% are glucuronide conjugates • Metabolism is primarily mediated by CYP3A and to a lesser extent by CYP2E and CYP2B/C • The metabolites of ethosuximide are not pharmacologically active • Autoinduction is not a feature of ethosuximide metabolism

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E

Elimination: • Half-life values of ethosuximide are 40–60 hours in adults and 30–40 hours in children • In patients co-prescribed enzyme-inducing antiepileptic drugs half-life values are 20–40 hours • Renal excretion:  ~20% of an administered dose is excreted unchanged in urine

Ethosuximide

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on ethosuximide: –– Carbamazepine, phenobarbital, phenytoin, and primidone can increase the clearance of ethosuximide and decrease ethosuximide plasma levels –– Valproic acid can decrease the clearance of ethosuximide and increase ethosuximide plasma levels • Interactions between AEDs: effects by ethosuximide: –– Ethosuximide can decrease plasma levels of valproic acid • Interactions between AEDs and non-AED drugs:  effects on ethosuximide: –– Rifampicin can decrease ethosuximide plasma levels –– Isoniazid and ritonavir can increase ethosuximide plasma levels • Interactions between AEDs and non-AED drugs:  effects by ethosuximide: –– To date, there have been no reports of ethosuximide affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • The combination of ethosuximide with valproic acid can lead to a favorable pharmacodynamic interaction which may allow control of absence seizures in patients not responsive to monotherapy with either drug Hormonal contraception: • Ethosuximide does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

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Adverse effects How drug causes adverse effects: • The mechanism by which ethosuximide causes adverse effects has not been established

the epilepsy prescriber’s guide to antiepileptic drugs Common adverse effects: • Abdominal discomfort • Vomiting, diarrhea • Hiccups • Headaches • Sedation, drowsiness, fatigue

E

Life-threatening or dangerous adverse effects: • Dose-related reversible granulocytopenia • More severe bone marrow reactions with granulocytopenia, thrombocytopenia, or pancytopenia • Systemic lupus erythematosus • Stevens-Johnson syndrome

Weight change: • Weight loss consequent to anorexia, nausea, vomiting and diarrhea may occur

Dosing and use

Rare and not life-threatening adverse effects: • Behavioral disturbances: nervousness, irritability, depression, hallucinations, and even psychosis • Psychosis has been found to occur in conjunction with eradication of seizure activity, a phenomenon for which the term “forced normalization” has been coined • Extrapyramidal reactions, such as dyskinesia

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Gastrointestinal adverse effects can improve when the medication is taken at the end of a meal • Gastrointestinal adverse effects can be minimized by undertaking a slow titration • Clinical alertness to possible signs and symptoms is likely to be more effective in recognizing hematological adverse effects than routine monitoring of the blood count

Dosing and use Usual dosage range: • Adults and children over 12 years of age: 600–1200 mg/day • Children under 12 years of age: 20–30 mg/kg/day Available formulations: • Capsules (liquid filled): 250 mg • Syrup: 250 mg/5 mL

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E

How to dose: • When initiating ethosuximide treatment start with a low dose and titrate slowly so as to minimize adverse effects, particularly gastrointestinal disturbances –– For adults and children over 12 years of age:  start treatment with 250 mg/day and increase at 5–7 day intervals in increments of 250 mg up to a total of 500–1250 mg/day, in two or three daily doses –– Children under 12 years of age: start treatment with 5–10 mg/kg/ day and slowly increase at 5–7 day intervals in increments of 10 mg/kg/day up to a total of 20–30 mg/kg/day

Ethosuximide

Dosing tips: • Ethosuximide should be ingested preferably after meals so as to minimize gastrointestinal symptoms • If the patient’s weight requires an increment of 125 mg, the capsules can be frozen and then easily cut in half • The total daily dose can be divided into two daily doses, or also into three daily doses if this makes it easier for the child to take the medication or if it can be shown to improve gastrointestinal adverse effects • When treatment of absence seizures is considered or re-considered in patients above the age of 10 years, a drug with the appropriate broader spectrum of activity should be used, such as valproate or lamotrigine; alternatively ethosuximide should be combined with another drug that does provide protection against generalized tonic–clonic seizures How to withdraw drug: • May need to adjust dosage of concurrent medications as ethosuximide is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Rapid discontinuation may increase the risk of seizures • Dose can be decreased linearly at weekly intervals over a period of 1–3 months • Because recurrence of absence seizures may be subtle clinically, or because significant sub-clinical spike-and-wave discharges may require re-introduction of therapy, it is good practice to repeat an EEG 1–3 months after ethosuximide has been discontinued

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Overdose: • Usually not fatal:  symptoms include nausea, vomiting, stupor, coma, respiratory depression • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes ethosuximide from blood (~50% over a 6-hour dialysis interval) and, therefore, serves as a useful procedure in cases of overdose

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E

Special populations

Tests and therapeutic drug monitoring: • Before starting: full blood count • There are no clear guidelines regarding the need to monitor blood counts for the rare occurrence of bone marrow suppression, and clinical education and observation is likely to provide the best probability of early detection; blood count can be determined after 2 months, then every 6 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at ethosuximide plasma levels of 40–100 mg/L (300–700 µmol/L), but levels below 40 mg/L may be fully effective, and levels as high as 150 mg/L may be necessary and well tolerated –– The conversion factor from mg/L to μmol/L is 7.06 (i.e., 1 mg/L = 7.06 μmol/L) –– Once the patient is doing well clinically, there is no need to determine blood levels routinely –– The reference range of ethosuximide in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Ethosuximide can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant Other warnings/precautions: • Patients should be monitored carefully for signs of unusual bleeding or bruising Do not use: • In patients with generalized tonic–clonic seizures unless they also take a medication that is known to be effective against tonic– clonic seizures

Special populations Renal impairment: • Approximately 20% of the ethosuximide dose is not metabolized and renally secreted, therefore, the dose may need to be lowered • Because ethosuximide can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of ethosuximide Hepatic impairment: • Ethosuximide is extensively metabolized in the liver and consequently lower doses may be required

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Ethosuximide 74

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults Elderly: • Ethosuximide is used only very rarely in the elderly • Elderly patients are more susceptible to adverse effects (especially somnolence) and, therefore, often do better at lower doses • Because of an age-related reduction in renal and hepatic function, lower ethosuximide doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with ethosuximide is moderate Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Ethosuximide is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than ethosuximide monotherapy • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of ethosuximide during pregnancy are conflicting; ethosuximide clearance can increase accompanied by a decrease in plasma ethosuximide concentrations Breast feeding • Breast milk: 50–80% of maternal plasma levels • Breastfed infants:  ethosuximide plasma levels are 30–50% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

the epilepsy prescriber’s guide to antiepileptic drugs The overall place of ethosuximide in the treatment of epilepsy Ethosuximide is the drug of first choice for the treatment of typical childhood absence seizures and is associated with a 70% seizure-free success rate as monotherapy. Ethosuximide should be considered as initial monotherapy only in those children with childhood absence epilepsy who have never experienced a generalized tonic–clonic seizure, against which ethosuximide has no protective effect and indeed may exacerbate.

Secondary seizure types: • Atypical absence seizures • Myoclonic seizures • Astatic seizures (drop attacks) Potential advantages: • Ethosuximide is among the best antiepileptic drugs for the treatment of childhood absence epilepsy • It has a mostly benign adverse effect profile and severe adverse reactions are extremely rare • Linear pharmacokinetics with a moderate interaction potential

Ethosuximide, overall role

Primary seizure types: • Typical childhood absence seizures

E

Potential disadvantages: • Narrow spectrum of seizure protection, limited mostly to absence seizures • Abrupt withdrawal in patients with absences may precipitate absence status epilepticus • Potential teratogen, but not more than most other antiepileptic drugs Suggested reading Callaghan N, O’Hare J, O’Driscoll D, O’Neill B, Dally M. Comparative study of ethosuximide and sodium valproate in the treatment of typical absence seizures (petit mal). Developmental Medicine and Child Neurology 1982; 24: 830–836. Capovilla G, Beccaria F, Veggiotti P, Rubboli G, Meletti S, Tassinari CA. Ethosuximide is effective in the treatment of epileptic negative myoclonus in childhood partial epilepsy. Journal of Child Neurology 1999; 14: 395–400. Giaccone M, Bartoli A, Gatti G, Marchiselli R, Pisani F, Latella MA, Perucca E. Effect of enzyme-inducing anticonvulsants on ethosuximide pharmacokinetics in epileptic patients. British Journal of Clinical Pharmacology 1996; 41: 575–579. Glaucer TA, Cnaan A, Shinnar S, Hirtz DG, Dlugos D, Masur D, Clark PO, Capparelli EV, Adamson PC. For the Childhood

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Ethosuximide 76

Absence Epilepsy Study Group. Ethosuximide, Valproic acid, and Lamotrigine in childhood absence epilepsy. New England Journal of Medicine 2010; 362: 790–799. Mattson RH, Cramer JA. Valproic acid and ethosuximide interaction. Annals of Neurology 1980; 7: 583–584. Panayiotopoulos CP. Treatment of typical absence seizures and related epileptic syndromes. Paediatric Drugs 2001; 3: 379–403. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Posner EB, Mohamed K, Marson AG. Ethosuximide, sodium valproate or lamotrigine for absence seizures in children and adolescents. Cochrane Database of Systematic Reviews 2005; 4: CD003032. Rowan AJ, Meiser JW, De-Beer-Pawlikowski N. Valproateethosuximide combination therapy for refractory absence seizures. Archives of Neurology 1983; 40: 797–802. Sato S, White BG, Penry JK, Dreifuss FE, Sackellares JC, Kupferberg HJ. Valproic acid versus ethosuximide in the treatment of absence seizures. Neurology 1982; 32: 157–163. Snead OC, Horsey L. Treatment of epileptic falling spells with ethosuximide. Brain Development 1987; 9: 602–604.

the epilepsy prescriber’s guide to antiepileptic drugs

Felbamate Therapeutics Chemical name and structure: Felbamate, 2-phenyl-1,3-propanediol dicarbamate, is an off-white crystalline powder, with a molecular weight of 238.24 and an empirical formula of C11H14N2O4.

F

O NH2 O

NH2 O Brand names: • Felbamyl; Felbatol • Taloxa

therapeutics

O

Generics available: • No Licensed indications for epilepsy: • Monotherapy or adjunctive therapy of partial and secondary generalized seizures in adults (FDA-PI) • Adjunctive therapy for the treatment of partial and generalized seizures associated with Lennox-Gastaut syndrome in children (FDA-PI) • Felbamate is recommended only in patients who responded inadequately to alternative treatments (FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • Absence seizures • Acquired epileptic aphasia (Landau-Kleffner syndrome) • Infantile spasms (West syndrome) • Juvenile myoclonic epilepsy Nonlicensed use for non-epilepsy conditions: • There are none

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F

Ineffective (contraindicated): • Because of its potentially serious adverse effects, felbamate is not indicated as first-line therapy for any type of seizure Mechanism of action: • Inhibits glycine-enhanced N-methyl-D-aspartate (NMDA)– induced intracellular calcium currents • Potentiates GABA responses at high felbamate concentrations • Inhibits excitatory NMDA responses at high felbamate con­ centrations • Effects use-dependent inhibition of NMDA currents (at therapeutic levels of 50–300 micromoles)

Felbamate

Efficacy profile: • The goal of treatment is complete remission of seizures • Onset of efficacy occurs mostly within the first 2 weeks of treatment • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • If felbamate does not provide significant seizure control within 2–3 months, it should be discontinued because of the associated risk of severe adverse effects • If felbamate is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Pharmacokinetics Absorption and distribution: • Oral bioavailability: >90% • Food co-ingestion:  neither delays the rate of absorption nor decreases the extent of absorption • Tmax: 2–6 hours • Time to steady state: 3–5 days • Pharmacokinetics: linear • Protein binding: 25% • Volume of distribution: 0.76 L/kg (adults); 0.91 L/kg (children) • Salivary concentrations:  it is not known whether felbamate is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

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Metabolism: • Only 50% of an administered dose is metabolized in the liver, by CYP3A4 and CYP2E1, to form two hydroxylated metabolites (para-hydroxyfelbamate and 2-hydroxyfelbamate  – 10–15%) and a variety of other unidentified polar metabolites, some of them being glucuronides or sulfate esters

the epilepsy prescriber’s guide to antiepileptic drugs • There is evidence to suggest that in humans the formation of several other metabolites, including atropaldehyde (2-phenylpropenal) may contribute to the cytotoxicity seen in some patients treated with felbamate • The metabolites of felbamate are not pharmacologically active • Autoinduction is not a feature of felbamate metabolism

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on felbamate: –– Carbamazepine, gabapentin, phenobarbital, phenytoin, and primidone can increase the clearance of felbamate and decrease felbamate plasma levels –– Valproic acid can decrease the clearance of felbamate and increase felbamate plasma levels • Interactions between AEDs: effects by felbamate: –– Felbamate can increase the plasma levels of carbamazepine-10, 11-epoxide, N-desmethyl-clobazam, methsuximide, phenytoin, phenobarbital, and valproic acid • Interactions between AEDs and non-AED drugs:  effects on felbamate: –– To date, there have been no reports of other non-AED drugs affecting the clearance of felbamate and affecting felbamate plasma levels • Interactions between AEDs and non-AED drugs:  effects by felbamate: –– Felbamate can decrease plasma levels of warfarin

Drug interaction profile

Elimination: • In adult volunteers felbamate half-life values are 16–22 hours • In patients co-prescribed enzyme-inducing antiepileptic drugs felbamate half-life values are 10–18 hours • Renal excretion:  ~50% of an administered dose is excreted unchanged in urine

F

Pharmacodynamic drug interactions: • To date, none have been reported Hormonal contraception: • Felbamate enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking felbamate

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F

Adverse effects How drug causes adverse effects: • Some metabolites, including atropaldehyde (2-phenylpropenal), are considered to contribute to the cytotoxicity associated with felbamate Common adverse effects: • Nausea, vomiting, anorexia, dyspepsia • Insomnia, irritability • Dizziness, somnolence, diplopia • Headache Life-threatening or dangerous adverse effects: • Aplastic anemia (risk may be >100 times above risk for general population; ~30–40% are fatal) • Hepatic failure (~50% fatal)

Felbamate

Rare and not life-threatening adverse effects: • Choreoathetosis • Dystonia • Kidney stones Weight change: • Weight loss commonly occurs

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What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Do not use felbamate in patients with a history of blood dyscrasia or hepatic dysfunction • Obtain complete blood count and transaminases at baseline, then at the latest 1 month after initiation of felbamate, then at least every 3 months • There is no evidence that such monitoring will allow detection of bone marrow suppression before aplastic anemia occurs • Clinical alertness to possible signs and symptoms is likely to be more effective in recognizing hematological adverse effects than routine monitoring of the blood count • The common adverse effects have a higher incidence in antiepileptic polytherapy than in monotherapy • Risk factors for aplastic anemia may include: age 18 years or above, female gender, cytopenia with previous antiepileptic drugs, polytherapy, and clinical or serological evidence of a concomitant immune disorder • If felbamate shows no effectiveness within 2–3 months in any given patient, discontinue its use

the epilepsy prescriber’s guide to antiepileptic drugs • Serious adverse effects have occurred mostly within the first 6 months of treatment, and are much less likely after 18 months of treatment

F

Dosing and use Usual dosage range: • Adults and children over 12 years of age: 2400–5000 mg/day • Children under 12 years of age: 30–60 mg/kg/day Available formulations: • Tablets: 400 mg, 600 mg • Suspension: 600 mg/5 mL

Dosing and use

How to dose: –– For adults and children over 12 years of age: start treatment with 1200 mg/day, twice daily, for 1 week; during the second week, increase to 2400 mg/day; during the third week of treatment, if necessary and if tolerated, the dose is to be increased to 3600 mg/day. If felbamate is introduced in a patient who is not taking an enzyme-inducing AED, a slower titration is recommended; in adults doses of 5000–6000 mg/day have been commonly used –– Children under 12 years of age: start treatment with 15 mg/kg/day, twice daily, for 1 week; during the second week, increase to 30 mg/kg/day; during the third week of treatment, if necessary and if tolerated, the dose is to be increased to 45 mg/kg/ day. If felbamate is introduced in a patient who is not taking an enzyme-inducing antiepileptic drug, a slower titration is recommended; maintenance doses may often safely exceed 45 mg/ kg/day Dosing tips: • Do not use felbamate in patients with a history of blood dyscrasia or hepatic dysfunction • To decrease adverse effects, the daily dose of concomitant anti­ epileptic drugs should be decreased by approximately one-fifth to one-third when felbamate is introduced • Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating effects • Whenever possible, try to achieve monotherapy with felbamate How to withdraw drug: • May need to adjust dosage of concurrent medications as felbamate is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Rapid discontinuation may increase the risk of seizures

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F

• Dose can be decreased at weekly intervals over a period of 1–3 months Overdose: • No serious adverse reactions have been reported at up to 12,000 mg in 12 hours • May cause crystalluria and even renal failure • If indicated the stomach should be emptied by lavage or by induction of emesis • It is not known whether hemodialysis removes felbamate from blood and, therefore, can serve as a useful procedure in cases of overdose

Felbamate

Tests and therapeutic drug monitoring: • Obtain complete blood count and transaminases at baseline, then at the latest 1 month after initiation of felbamate, then at least every 3 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at felbamate plasma levels of 30–60 mg/L (125–250 μmol/L) –– The conversion factor from mg/L to μmol/L is 4.20 (i.e., 1 mg/L = 4.20 μmol/L) –– The reference range of felbamate in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– It is not known whether felbamate can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant Other warnings/precautions: • Patients should be monitored carefully for signs of unusual bleeding or bruising • Obtain liver function test in cases of symptoms suggestive of felbamate hepatotoxicity, which include nausea, vomiting, anorexia, lethargy, jaundice, and at times loss of seizure control

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Do not use: • In patients with a history of blood dyscrasia or hepatic dysfunction • Because of its potentially serious adverse effects, felbamate is not indicated as first-line therapy for any type of seizure • If patient has a proven allergy to felbamate or to any of the ­excipients – tablets contain lactose • Because the tablet formulation contains lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency or glucose–galactose malabsorption should not take this formulation

the epilepsy prescriber’s guide to antiepileptic drugs Special populations Renal impairment: • Felbamate is renally excreted (~50%) and, therefore, the dose may need to be lowered

F

Hepatic impairment: • Felbamate undergoes moderate metabolism (~50%) in the liver and consequently lower doses may be required

Elderly: • No systematic studies in elderly patients have been conducted • Elderly patients are more susceptible to adverse effects of antiepileptic drugs (especially somnolence) and, therefore, often do better at lower doses • Because of an age-related reduction in renal and hepatic function, lower felbamate doses may be appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with felbamate is moderate Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Felbamate is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Taper drug if discontinuing

Special populations

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults • Risk of fatal hepatotoxicity is similar for all age groups • Fatal aplastic anemia has not been reported in any patient younger than 18 years

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F

• Seizures, even mild seizures, may cause harm to the embryo/fetus • There are no data on the pharmacokinetic changes of felbamate during pregnancy Breast feeding • Breast milk: felbamate has been detected in human breast milk • Breastfed infants: it is not known what plasma felbamate concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

Felbamate

The overall place of felbamate in the treatment of epilepsy The clinical use of felbamate has been significantly compromised consequent to its association with a high incidence of aplastic anemia and hepatic failure which resulted in several fatalities. Presently, felbamate is never considered as a first-line therapy for any seizure type and should only be prescribed to patients who respond inadequately to alternative antiepileptic drugs and whose epilepsy is so severe that a substantial risk of aplastic anemia and/or liver failure is deemed acceptable in light of the benefits conferred by its use. In this setting, felbamate can be considered in combination therapy or in monotherapy for the treatment of the Lennox-Gastaut syndrome and of partial seizures with or without secondary generalization. Primary seizure types: • Partial seizures with or without secondary generalization • Lennox-Gastaut syndrome Secondary seizure types: • Myoclonic seizures • Infantile spasms (West syndrome) Potential advantages: • Felbamate probably has a broad spectrum of seizure protection • Felbamate may be one of the more effective drugs in the treatment of Lennox-Gastaut syndrome

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Potential disadvantages: • Relatively high incidence of two potentially life-threatening adverse effects, aplastic anemia, and liver failure • Requires frequent blood testing and close monitoring • Associated with significant pharmacokinetic interactions and usually acts as an inhibitor of hepatic metabolism • Potential teratogen, but not more than most other antiepileptic drugs

the epilepsy prescriber’s guide to antiepileptic drugs

F

Felbamate, overall role

Suggested reading Faught E, Sachdeo RC, Remler MP, Chayasirisobhon S, Iraqui-Madoz VJ, Ramsay RE, Sutula TP, Kanner A, Harner RN, Kuzniecki R. Felbamate monotherapy for partial-onset seizures: an activecontrol trial. Neurology 1993; 43: 688–692. French J, Smith M, Faught E, Brown L. The use of felbamate in the treatment of patients with intractable epilepsy: practice advisory. Neurology 1999; 52: 1540–1545. Harden CL, Trifiletti R, Kutt H. Felbamate levels in patients with epilepsy. Epilepsia 1996; 37: 280–283. Hurst DL, Rolan TD. The use of felbamate to treat infantile spasms. Journal of Child Neurology 1995; 10: 134–136. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. Kaufman DW, Kelly JP, Anderson T, Harmon DC, Shapiro S. Evaluation of case reports of aplastic anemia among patients treated with felbamate. Epilepsia 1997; 38: 1265–1269. O’Neil MG, Perdun CS, Wilson MB, McGown ST, Patel S. Felbamate-associated fatal acute hepatic necrosis. Neurology 1996; 46: 1457–1459. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Pellock JM, Faught E, Leppik IE, Shinnar S, Zupanc ML. Felbamate:  consensus of current clinical experience. Epilepsy Research 2006; 71: 89–101. The Felbamate Study Group in Lennox-Gastaut syndrome. Efficacy of felbamate in childhood epileptic encephalopathy (Lennox-Gastaut syndrome). New England Journal of Medicine 1993; 328: 29–33.

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F

Fosphenytoin Therapeutics Chemical name and structure: Fosphenytoin, a disodium phosphate ester of 3-hydroxymethyl-5,5diphenylhydantoin, is a white powder, with a molecular weight of 406.24 and an empirical formula of C16H15N2O6P. It is an injectable prodrug of phenytoin.

O NCH2OPO3Na2

HN

Fosphenytoin

O Brand names: • Cerebyx • Fosolin • Prodilantin; Pro-Epanutin Generics available: • No Licensed indications for epilepsy: • Control of generalized convulsive status epilepticus (UK-SPC; FDA-PI) • Prevention of seizures occurring during neurosurgery and/or head trauma (UK-SPC; FDA-PI) • As a substitute, short-term, for oral phenytoin if oral administration is not possible and/or contraindicated (UK-SPC; FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • There are none

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Ineffective (contraindicated): • Intramuscular administration of fosphenytoin is contraindicated in the treatment of status epilepticus

the epilepsy prescriber’s guide to antiepileptic drugs • Because phenytoin is ineffective against absence seizures, if tonic– clonic seizures are present simultaneously with absence seizures, combined drug therapy is recommended • Fosphenytoin is not used chronically in the treatment of epileptic seizures

Efficacy profile: • Fosphenytoin is a valuable alternative to parenteral phenytoin • It is for the treatment of status epilepticus and for the prophylaxis of serial seizures • If fosphenytoin does not terminate seizures, the use of alternative antiepileptic drugs should be considered

Pharmacokinetics

Mechanism of action: • Fosphenytoin is a prodrug of phenytoin and, therefore, its anticonvulsant effects are those attributable to phenytoin • Acts as a use-dependent blocker of voltage-sensitive sodium channels • Interacts with the open channel conformation of voltage-sensitive sodium channels • Modulates sustained repetitive firing • Regulates calmodulin and second messenger systems • Inhibits calcium channels and calcium sequestration

F

Pharmacokinetics Absorption and distribution: • Bioavailability: 100% (intramuscular administration) • Tmax: fosphenytoin: at end of infusion following intravenous administration; ~0.5 hours following intramuscular administration • Tmax: phenytoin: 0.5–1.0 hours following the start of intravenous infusion; 1.5–4 hours following intramuscular administration • Time to steady state: 6–21 days (phenytoin) • Pharmacokinetics: nonlinear due to saturable metabolism so that clearance decreases with increasing dose • Protein binding: fosphenytoin: 95–99%; phenytoin: 90% • Volume of distribution: 0.04–0.13 L/kg Metabolism: • Fosphenytoin undergoes hydrolysis by phosphatase enzymes, present in liver, red blood cells and other tissues, to form phenytoin and two metabolites, namely phosphate and formaldehyde • Formaldehyde is subsequently converted to formate, which is further metabolized by means of folate dependent pathways • The half-life for conversion of fosphenytoin to phenytoin is 8–15 minutes • The derived phenytoin undergoes metabolism in the same way as when phenytoin is administered as such (see Phenytoin section)

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F

Elimination: • The derived phenytoin undergoes elimination in the same way as when phenytoin is administered as such (see Phenytoin section) • Renal excretion:  <4% of an administered dose is excreted as unchanged fosphenytoin in urine

Drug interaction profile There are no drugs known to interfere with the conversion of fosphenytoin to phenytoin

Fosphenytoin

Pharmacokinetic drug interactions: • Interactions between AEDs: effects on phenytoin: –– Fosphenytoin can displace phenytoin from its plasma protein binding sites and increase free nonprotein bound phenytoin levels –– Drug interactions which may occur following the administration of fosphenytoin are those that are expected to occur with drugs known to interact with phenytoin (see Phenytoin section) • Interactions between AEDs: effects by phenytoin: –– Drug interactions which may occur following the administration of fosphenytoin are those that are expected to occur with drugs known to interact with phenytoin (see Phenytoin section) • Interactions between AEDs and non-AED drugs:  effects on phenytoin: –– Drug interactions which may occur following the administration of fosphenytoin are those that are expected to occur with drugs known to interact with phenytoin (see Phenytoin section) • Interactions between AEDs and non-AED drugs:  effects by phenytoin: –– Drug interactions which may occur following the administration of fosphenytoin are those that are expected to occur with drugs known to interact with phenytoin (see Phenytoin section) Pharmacodynamic drug interactions: • To date, none have been identified

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Hormonal contraception: • Although it is not known whether or not fosphenytoin affects hormonal contraceptives, phenytoin enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are, therefore, indicated in patients taking fosphenytoin

the epilepsy prescriber’s guide to antiepileptic drugs Adverse effects How drug causes adverse effects: • Fosphenytoin is a prodrug of phenytoin and, therefore, the mechanisms whereby adverse effects occur are those attributable to phenytoin (see Phenytoin section)

F

Common adverse effects: • Fosphenytoin is a prodrug of phenytoin and, therefore, its adverse effects are those attributable to phenytoin (see Phenytoin section)

Rare and not life-threatening adverse effects: • See Phenytoin section Weight change; • See Phenytoin section

Dosing and use

Life-threatening or dangerous adverse effects: • See Phenytoin section • Fosphenytoin should be used with caution in patients with hypotension and severe myocardial insufficiency because severe cardiovascular reactions including atrial and ventricular conduction depression and ventricular fibrillation, and sometimes fatalities, have occurred following fosphenytoin administration

What to do about adverse effects: • Dosage reduction in cases of presumably dose-related adverse effects • Hypotension may occur following intravenous administration of high doses and/or high infusion rates of fosphenytoin, even within recommended doses and rates; a reduction in the rate of administration or discontinuation of dosing may be necessary

Dosing and use Doses of fosphenytoin are always expressed as their phenytoin sodium equivalent (PE) to avoid the need to perform molecular weightbased adjustments when substituting fosphenytoin for phenytoin or vice versa; 1.5 mg of fosphenytoin is equivalent to 1 mg PE Usual dosage range: • In status epilepticus: –– iv loading dose: 15 mg PE/kg and an infusion rate of 100–150 mg PE/min  – adults; 15 mg PE/kg and an infusion rate of 2–3 mg/kg/min – children –– iv or im maintenance dose: 4–5 mg PE/kg/day; iv infusion rate 50–100 mg PE/min  – adults; 4–5 mg PE/kg/day; iv infusion rate 1–2 mg PE/kg/min – children

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F

• In treatment or prophylaxis of seizures: –– iv or im loading dose: 10–15 mg PE/kg and an infusion rate of 50–100 mg PE/min – adults; 10–15 mg PE/kg and an infusion rate of 1–2 mg/kg/min – children –– iv or im maintenance dose: 4–5 mg PE/kg/day; iv infusion rate 50–100 mg PE/min  – adults; 4–5 mg PE/kg/day; iv infusion rate 1–2 mg PE/kg/min – children Available formulations: • Solution for injection:  750 mg/10 mL (equivalent to 500 mg of phenytoin sodium and referred to as 500 mg PE [phenytoin equivalent])

Fosphenytoin 90

How to dose: • Intravenous administration is essential for the management of status epilepticus whereby either intravenous or intramuscular administration can be used in the treatment or prophylaxis of seizures • In status epilepticus: –– For adults: start treatment with a loading dose of 20 mg PE/kg administered as a single dose by iv infusion; the recommended iv infusion rate is 100–150 mg PE/min and should not exceed 150 mg PE/min; maintenance dose is 4–5 mg PE/kg/day and may be administered by iv infusion or by im injection in one or two divided doses; iv infusion rate is 50–100 mg PE/min and should not exceed 100 mg PE/min –– Children 5 years and above: start treatment with a loading dose of 20 mg PE/kg administered as a single dose by iv infusion; the recommended iv infusion rate is 2–3 mg/kg/min and should not exceed 3 mg PE/kg/min or 150 mg PE/min; maintenance dose is 4–5 mg PE/kg/day and may be administered by iv infusion in one or two divided doses; iv infusion rate is 1–2 mg PE/kg/ minute and should not exceed 100 mg PE/min • In treatment or prophylaxis of seizures: –– For adults: start treatment with a loading dose of 10–15 mg PE/ kg administered as a single dose by iv infusion or by im injection; the recommended iv infusion rate is 100–150 mg PE/min and should not exceed 150 mg PE/min; maintenance dose is 4–5 mg PE/kg/day and may be administered by iv infusion or by im injection in one or two divided doses; iv infusion rate is 50–100 mg PE/min and should not exceed 100 mg PE/min –– Children 5 years and above: start treatment with a loading dose of 10–15 mg PE/kg administered as a single dose by iv infusion, the recommended iv infusion rate is 1–2 mg/kg/min and should not exceed 3 mg PE/kg/min or 150 mg PE/min; maintenance dose is 4–5 mg PE/kg/day and may be administered by iv infusion in one to four divided doses; iv infusion rate is 1–2 mg PE/ kg/min and should not exceed 100 mg PE/min

the epilepsy prescriber’s guide to antiepileptic drugs

How to withdraw drug: • May need to adjust dosage of concurrent medications as fosphenytoin is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper:  a gradual dose reduction over a period of many weeks should be undertaken • Rapid discontinuation may induce withdrawal seizures and should only be undertaken if there are safety concerns (e.g., a rash with serious characteristics)

F

Dosing and use

Dosing tips: • Before intravenous infusion fosphenytoin should be diluted in 5% glucose/dextrose or 0.9% saline so that the concentration ranges from 1.5–2.5 mg PE/mL • Transient itching, burning, warmth or tingling in the groin during and shortly after intravenous infusion of fosphenytoin can be avoided or minimized by using a slower rate of infusion or by temporarily stopping the infusion • Intramuscular administration should not be used in the treatment of status epilepticus because the attainment of peak fosphenytoin and phenytoin plasma levels is delayed • Because of the risk of hypotension, the recommended rate of administration by iv infusion in routine clinical settings is 50–100 mg PE/min and it should not exceed 150 mg PE/min even in the emergency situation as occurs with status epilepticus • Cardiac resuscitation equipment should be available and continuous monitoring of electrocardiogram, blood pressure, and respiratory function for the duration of the infusion is essential; the patient should also be observed throughout the period where maximum plasma phenytoin levels occur (~30 minutes after the end of infusion period)

Overdose: • Initial symptoms of fosphenytoin toxicity are those associated with phenytoin and include ataxia, nystagmus and dysarthria; subsequently the patient becomes comatose, the pupils are unresponsive and hypotension occurs followed by respiratory depression and apnea; death is the consequence of respiratory and circulatory depression • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes phenytoin from blood and, therefore, serves as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Therapeutic drug monitoring: –– Fosphenytoin plasma levels are not necessary or helpful to guide patient management 91

the epilepsy prescriber’s guide to antiepileptic drugs

F

–– Optimum seizure control is most likely to occur at plasma phenytoin concentrations of 10–20 mg/L (40–80 μmol/L); however, many patients in status epilepticus often require higher levels (up to 30 mg/mL [120 μmol/L]) –– The conversion factor from mg/L to μmol/L is 3.96 (i.e., 1 mg/L = 3.96 μmol/L) Other warnings/precautions: • Life-threatening rashes have developed in association with phenytoin use; fosphenytoin should generally be discontinued at the first sign of serious rash • See Phenytoin section Do not use:

• If patient has a proven allergy to fosphenytoin, phenytoin, or to any of the excipients

Fosphenytoin

Special populations Renal impairment: • Except in the treatment of status epilepticus, a lower loading dose and/or infusion rate and lower or less frequent maintenance dose may be required in renally impaired patients; a 10–25% reduction in dose or rate may be considered and clinical monitoring is essential • The conversion rate of fosphenytoin to phenytoin may be increased • Plasma unbound phenytoin levels may also be increased and patient management may best be guided by monitoring free nonprotein bound levels • Because phenytoin can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of fos­ phenytoin Hepatic impairment: • Except in the treatment of status epilepticus, a lower loading dose and/or infusion rate and lower or less frequent maintenance dose may be required in renally impaired patients; a 10–25% reduction in dose or rate may be considered and careful clinical monitoring is essential • The conversion rate of fosphenytoin to phenytoin may be increased • Plasma unbound phenytoin levels may also be increased and patient management may best be guided by monitoring free nonprotein bound levels

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Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults

the epilepsy prescriber’s guide to antiepileptic drugs Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in hepatic function, a lower loading dose and/or infusion rate and a lower or less frequent maintenance dose may be required; a 10–25% reduction in dose or rate may be considered and careful clinical monitoring is essential

Fosphenytoin, overall role

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Fosphenytoin is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Seizures, even mild seizures, may cause harm to the embryo/fetus • It is not known whether the pharmacokinetics of fosphenytoin change during pregnancy, but the pharmacokinetics of phenytoin change significantly (see Phenytoin section)

F

Breast feeding: • Breast milk: it is not known whether fosphenytoin is excreted in breast milk; phenytoin – 10–60% of maternal plasma levels • Breastfed infants: it is not known what plasma fosphenytoin concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (irritability or sedation) • If adverse effects are observed recommend bottle feed

The overall place of fosphenytoin in the treatment of epilepsy Although phenytoin is an invaluable antiepileptic drug for the management of acute seizures and status epilepticus its parenteral formulation has numerous disadvantages including toxicity and administration problems. This can be attributed to the fact that it is water insoluble and is formulated in propylene glycol and alcohol and has a pH of 14. Fosphenytoin, in contrast, is water soluble and has a physiological pH and is easier and quicker to administer intravenously. The good tolerability of intramuscular fosphenytoin allows its use in clinical settings where prompt administration is indicated but secure intravenous access and cardiac monitoring are not available.

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F

Fosphenytoin is a well-tolerated and effective alternative to parenteral phenytoin in the emergency and nonemergency management of acute seizures in children and adults. It is often considered the drug of choice for the management of established status epilepticus. Primary seizure types: • Generalized tonic–clonic seizures Secondary seizure types: • Partial seizures Potential advantages: • A useful alternative to parenteral phenytoin • Better tolerated at the injection site and has the same speed of action as parenteral phenytoin

Fosphenytoin 94

Potential disadvantages: • Phenytoin is the pharmacologically active metabolite of fosphenytoin and dosing needs to be guided by therapeutic drug monitoring (measurement of blood levels) of phenytoin • Phenytoin pharmacokinetics are not linear due to saturable metabolism • Administration requires that cardiac resuscitation equipment is available and continuous monitoring of electrocardiogram, blood pressure, and respiratory function for the duration of the infusion is essential • Dosing units (milligrams of phenytoin equivalents) can be confusing

Suggested reading Aweeka FT, Gottwald MD, Gambertoglio JG, Wright TL, Boyer TD, Pollock AS, Eldon MA, Kuglar AR, Alldredge BK. Pharmacokinetics of fosphenytoin in patients with hepatic or renal disease. Epilepsia 1999; 40: 777–782. Boucher BA, Bombassaro A, Rasmussen SN, Watridge CB, Achari R, Turlapaty P. Phenytoin prodrug 3-phosphoryloxy-methyl phenytoin (ACC-9653):  pharmacokinetics in patients following intravenous and intramuscular administration. Journal of Pharmacological Sciences 1989; 78: 923–932. Eldon MA, Loewen GR, Voigtman RE, Holmes GB, Hunt TL, Sedman AJ. Safety, tolerance, and pharmacokinetics of intravenous fosphenytoin. Clinical Pharmacology and Therapeutics 1993; 53: 212. Leppik IE, Boucher BA, Wilder BJ, Murthy VS, Watridge C, Graves NM, Rask CA, Turlapaty P. Pharmacokinetics and safety of a phenytoin prodrug given IV in patients. Neurology 1990; 40: 456–460. Pryor FM, Gidal B, Ramsay RE, DeToledo J, Morgan RO. Fosphenytoin: pharmacokinetics and tolerance of intramuscular loading doses. Epilepsia 2001; 42: 245–250.

the epilepsy prescriber’s guide to antiepileptic drugs

Gabapentin Therapeutics Chemical name and structure: Gabapentin, 1-(aminomethyl)-cyclohexaneacetic acid, is a crystalline substance, with a molecular weight of 171.23 and an empirical formula of C9H17NO2 .

G

HO

H2N

O

therapeutics

Brand names: • Alpentin • Bapex; Blugat • Calmpent • Dineurin • Engaba; Epiven; Epleptin • Gabadin; Gabahexal; Gabalep; Gabalept; Gabantin; Gabapenin; Gabatin; Gabatine; Gabax; Gabexol; Gabietal; Gabix; Ganin; Gantin; Gapatin; Gapridol; Gaty • Kaptin • Nepatic; Neuril; Neurontin; New-GABA; Nopatic; Nupentin • Pendine; Pengatine • Reinin • Vultin Generics available: • Yes Licensed indications for epilepsy: • Adjunctive treatment of partial seizures with or without secondary generalization in adults and children aged 6 years and above (UK-SPC) • Adjunctive treatment of partial seizures with or without secondary generalization in adults and children aged 12 years and above (FDA-PI) • Monotherapy treatment of partial seizures with or without secondary generalization in adults and children aged 12 years and above (UK-SPC) • Adjunctive treatment of partial seizures in children aged 3–12 years (FDA-PI)

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G

Licensed indications for non-epilepsy conditions: • Peripheral neuropathic pain (UK-SPC) • Postherpetic neuralgia in adults (FDA-PI) Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • Anxiety • Bipolar disorder • Trigeminal neuralgia

Gabapentin

Ineffective (contraindicated): • It is ineffective or may exaggerate generalized-onset seizures of any type, e.g., absences, myoclonic jerks, generalized tonic–clonic seizures • Should be used with caution in patients with mixed seizures including absences Mechanism of action: • Binds to the α2-δ protein subunit of voltage-gated calcium channels • This closes N and P/Q presynaptic calcium channels, diminishing excessive neuronal activity and neurotransmitter release • Although structurally related to GABA, it does not directly act on GABA or its receptors Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 2 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If gabapentin is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: <60% • Food co-ingestion:  decreases the extent of absorption (25–30%) and absorption is delayed by ~2.5 hours • As a leucine analog, gabapentin is transported both into the blood from the gut and also across the blood–brain barrier into the brain from the blood by the system L transport system (a sodium­independent transporter) • Tmax: 2–3 hours • Time to steady state: 1–2 days

the epilepsy prescriber’s guide to antiepileptic drugs • Pharmacokinetics: nonlinear due to saturable absorption • Protein binding: 0% • Volume of distribution: 0.65–1.04 L/kg • Salivary concentrations: gabapentin is secreted into saliva and concentrations are similar to the unbound levels seen in plasma

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Metabolism: • Gabapentin is not metabolized

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on gabapentin: –– To date, there have been no reports of AEDs affecting the clearance of gabapentin and affecting gabapentin plasma levels • Interactions between AEDs: effects by gabapentin: –– To date, there have been no reports of gabapentin affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on gabapentin: –– Antacids (Maalox, aluminum hydroxide, magnesium hydroxide) can reduce oral bioavailability of gabapentin and decrease gabapentin plasma levels –– Cimetidine, morphine and hydrocodone can decrease the clearance of gabapentin and increase gabapentin plasma levels –– Naproxen can enhance the absorption of gabapentin and increase gabapentin plasma levels • Interactions between AEDs and non-AED drugs:  effects by gabapentin: –– To date, there have been no reports of gabapentin affecting the clearance of other non-AED drugs and affecting their plasma levels

Drug interaction profile

Elimination: • Following a single dose, half-life values are 5–9 hours • The renal clearance of gabapentin is proportional to the creatinine clearance • Renal excretion:  100% of an administered dose is excreted unchanged in urine

Pharmacodynamic drug interactions: • To date, none have been reported Hormonal contraception: • Gabapentin does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

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G

Adverse effects How drug causes adverse effects: • CNS adverse effects may be due to excessive blockade of voltagesensitive calcium channels Common adverse effects: • Somnolence, dizziness, ataxia, fatigue, nystagmus, tremor • Vomiting, dyspepsia, diarrhea, constipation, anorexia, increased appetite, dry mouth • Blurred vision, diplopia, vertigo • Facial edema, purpura, rash, pruritus, acne • Impotence • Additional effects in children under age 12 include:  aggressive behavior, emotional lability, hyperkinesia, thought disorder, respiratory tract infections, otitis media, bronchitis

Gabapentin

Life-threatening or dangerous adverse effects: • Caution is recommended in patients with a history of psychotic illness • Some patients may experience acute pancreatitis • Patients on hemodialysis due to end-stage renal failure may develop myopathy with elevated creatinine kinase • Rarely rash, leukopenia and EEG changes and angina • May unmask myasthenia gravis Rare and not life-threatening adverse effects: • To date, none have been reported Weight change: • Weight gain is common What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Sedation is dose-related and can be problematic at high doses • Sedation can subside with time, but may not at high doses • Take more of the dose at night to reduce daytime sedation

Dosing and use Usual dosage range: • Adults and children over 12 years of age: 900–3600 mg/day • Children 3–12 years of age: 25–40 mg/kg/day

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Available formulations: • Capsules: 100 mg, 300 mg, 400 mg • Tablets: 600 mg, 800 mg

the epilepsy prescriber’s guide to antiepileptic drugs

Dosing tips: • Titration of dose can be undertaken rapidly, usually maintenance dosages can be achieved within a week, and should be undertaken based on individual tolerability and response to the drug • In patients with poor general health (e.g., low body weight, organ transplantation) the dose should be titrated more slowly, either by using smaller dosage strengths or longer intervals between dosage increases • Co-administration of gabapentin with antacids containing aluminum and magnesium, reduces gabapentin bioavailability by ~25% – this can be avoided by delaying gabapentin ingestion until at least after 2 hours after antacid ingestion

G

Dosing and use

How to dose: • When initiating gabapentin treatment start with a low dose and titrate slowly so as to minimize adverse effects. –– For adults and children over 12 years of age: start treatment with 300 mg/day on day 1; subsequently increase to 300 mg twice daily on day 2; subsequently increase to 300 mg thrice daily on day 3; increase subsequently according to response in steps of 300 mg in three divided doses; maintenance dose generally not greater than 3600 mg/day given in three equally divided doses –– Children:  6–12 years of age:  start treatment only as adjunctive therapy with 10–15 mg/kg daily in three divided doses; subsequently increase according to response over 3 days in steps of 10 mg/kg daily in three divided doses; maintenance dose is generally 25–35 mg/kg/day given in three equally divided doses –– Children:  3–5 years of age:  start treatment only as adjunctive therapy with 10–15 mg/kg daily in three divided doses; subsequently increase over 3 days to 40 mg/kg/day; maximum dose generally 50 mg/kg/day; time between any two doses should usually not exceed 12 hours

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as gaba­ pentin is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Taper: a gradual dose reduction over a minimum of a 1-week period should be undertaken • Rapid discontinuation may induce withdrawal seizures Overdose: • In overdoses up to 49 g, life-threatening adverse effects have not been observed • The most common adverse effects observed with gabapentin overdose include dizziness, double vision, slurred speech, drowsiness, lethargy, mild diarrhea

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• Reduced absorption of gabapentin at higher doses (due to saturable absorption) probably limits drug absorption and hence minimizes toxicity • Overdoses of gabapentin in combination with other CNS depressant medications may result in coma • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes gabapentin from blood (30–40% over 4 hours) and, therefore, may be a useful procedure in cases of overdose

Gabapentin

Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests • During treatment:  liver and kidney function tests every 6–12 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at gabapentin plasma concentrations of 2–20 mg/L (12–117 μmol/L) –– The conversion factor from mg/L to μmol/L is 5.84 (i.e., 1 mg/L = 5.84 μmol/L) –– The reference range of gabapentin in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Gabapentin can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant • Before giving a drug that can cause weight gain to an overweight or obese patient, consider determining whether the patient already has pre-diabetes (fasting plasma glucose 100–125 mg/dL), diabetes (fasting plasma glucose greater than 126 mg/dL), or dyslipidemia (increased total cholesterol, LDL cholesterol, and triglycerides; decreased HDL cholesterol), and treat or refer such patients for treatment, including nutrition and weight management, physical activity counseling, smoking cessation, and medical management • Monitor weight and BMI during treatment Other warnings/precautions: • Some diabetic patients who gain weight on gabapentin treatment may need to adjust their hypoglycemic medications • Some patients may experience dizziness and somnolence and thus caution needs to be exercised if patient intends to drive or use machinery

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Do not use: • If patient has a proven allergy to gabapentin or pregabalin or to any of the excipients – capsules contain lactose • Because the capsule formulation contains lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency, or glucose–galactose malabsorption should not take this formulation

the epilepsy prescriber’s guide to antiepileptic drugs

For patients with CrCL of <15 mL/min, the daily dose should be reduced in proportion to creatinine clearance. For example, patients with a CrCL of 7.5 mL/min should receive half the daily dose that patients with a CrCL of 15 mL/min receive • Because gabapentin can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of gabapentin Hepatic impairment: • Because gabapentin is not metabolized and is excreted predominantly as unchanged drug in urine, dosage adjustment will not be necessary in patients with hepatic impairment

G

Special populations

Special populations Renal impairment: • Gabapentin is renally excreted, so the dose needs to be adjusted according to creatinine clearance as follows: –– CrCL of ≥ 80 mL/min – total daily dose: 900–3600 mg/day taken three times a day –– CrCL of 50–79 mL/min  – total daily dose:  600–1800 mg/day taken three times a day –– CrCL of 30–49 mL/min  – total daily dose:  300–900 mg/day taken three times a day –– CrCL of 15–29 mL/min  – total daily dose:  150–600 mg/day taken as 300 mg every other day –– CrCL of <15 mL/min – total daily dose: 150–300 mg/day taken as 300 mg every other day

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal function, lower gabapentin doses are appropriate and should be based on creatinine clearance values • Because gabapentin is associated with dizziness and somnolence the elderly are at increased risk of accidental injury (fall) • The elderly have an increased risk of somnolence, peripheral edema and asthenia • Invariably the elderly are prescribed drug therapies for concurrent comorbidities, but the risk of pharmacokinetic interactions with gabapentin is low or nonexistent Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all

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antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Gabapentin is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than gabapentin monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Gabapentin pharmacokinetics do not change during pregnancy

Gabapentin

Breast feeding • Breast milk:  the milk/maternal blood concentration ratio is 0.7–1.3 • Breastfed infants: gabapentin plasma levels are 4–12% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (irritability or sedation), including hematological effects • If adverse effects are observed recommend bottle feed

The overall place of gabapentin in the treatment of epilepsy Gabapentin appears to be a narrow-spectrum antiepileptic drug whose role in the management of partial seizures is limited because its efficacy is weak compared with other antiepileptic drugs. The number of patients that respond to gabapentin is disproportionately low even when higher doses are used and it is rare for patients with severe focal epilepsies to derive therapeutic benefit. Primary seizure types: • Partial seizures Secondary seizure types: • None

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Potential advantages: • Gabapentin is generally well-tolerated, with only mild adverse effects • Not associated with any significant pharmacokinetic interactions

the epilepsy prescriber’s guide to antiepileptic drugs Potential disadvantages: • Less potent and less well-tolerated than pregabalin • Exaggerates absences, myoclonic jerks, and generalized tonic– clonic seizures • Requires three times a day dosing • Pharmacokinetics are not linear due to saturable absorption • Potential teratogen, but not more than most other antiepileptic drugs

Gabapentin, overall role

Suggested reading Boneva N, Brenner T, Argov Z. Gabapentin may be hazardous in myasthenia gravis. Muscle and Nerve 2000; 23: 1204–1208. Chadwick D, Leiderman DB, Sauermann W, Alexander J, Garofalo E. Gabapentin in generalized seizures. Epilepsy Research 1996; 25: 191–197. Fink K, Dooley DJ, Meder WP, Suman-Chauhan N, Duffy S, Clusmann H, Gothert M. Inhibition of neuronal Ca(2+) influx by gabapentin and pregabalin in the human neocortex. Neuropharmacology 2002; 42: 229–236. Gidal BE, Radulovic LL, Kruger S, Rutecki P, Pitterle M, Bockbrader HN. Inter- and intra-subject variability in gaba­ pentin absorption and absolute bioavailability. Epilepsy Research 2000; 40: 123–127. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. McLean MJ, Gidal BE. Gabapentin dosing in the treatment of epilepsy. Clinical Therapeutics 2003; 25: 1382–1406. Ohman I, Vitolis S, Tomson T. Pharmacokinetics of gabapentin during delivery, in the neonatal period and lactation. Epilepsia 2005; 46: 1621–1624. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Vollmer KO, von Hodenberg A, Kölle EU. Pharmacokinetics and metabolism of gabapentin in rat, dog and man. Arzneim Forsch Drug Research 1988; 36: 830–839. Wolf SM, Shinner S, Kang H, Gil KB, Moshe SL. Gabapentin toxicity in children manifesting as behavioural changes. Epilepsia 1995; 36: 1203–1205.

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Lacosamide Therapeutics Chemical name and structure: Lacosamide,   ( R)-2-acetamido-N-benzyl-3-methoxypropramide, is a white powder, with a molecular weight of 250.29 and an empirical formula of C13H18N2O3. OCH3

O H3C

N H

H N

* O

Lacosamide

Brand names: • Vimpat Generics available: • No Licensed indications for epilepsy: • Adjunctive treatment of partial onset seizures with or without secondary generalization in patients with epilepsy aged 16 years and older (UK-SPC) • Adjunctive treatment of partial onset seizures with or without secondary generalization in patients with epilepsy aged ≥17 years and older (FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • Nonconvulsive status epilepticus Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Data on seizure contraindications are not available

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Mechanism of action: • Acts by enhancing slow inactivation of voltage-gated sodium channels resulting in stabilization of hyperexcitable neuronal membranes • Binds to collapsing response mediator protein-2 (CRMP-2), a phosphoprotein which is primarily expressed in the nervous

the epilepsy prescriber’s guide to antiepileptic drugs system and is involved in neuronal differentiation and control of axonal outgrowth • The latter mechanism has been suggested to mediate a putative neuroprotective effect and to prevent neurodegenerative

Pharmacokinetics Absorption and distribution: • Oral bioavailability: 100% • Food co-ingestion:  neither delays the rate of absorption nor decreases the extent of absorption • Tmax: 1–2 hours • Time to steady state: 2–3 days • Pharmacokinetics: linear • Protein binding: <15% • Volume of distribution: 0.6–0.7 L/kg • Salivary concentrations: lacosamide is secreted into saliva and concentrations are similar to the unbound levels seen in plasma

Drug interaction profile

Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 4 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If lacosamide is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Metabolism: • Metabolized in the liver, by demethylation, to O-desmethyl lacosamide (30%) • CYP2C19 is considered to be primarily responsible for the formation of O-desmethyl lacosamide • Other unidentified metabolites constitute a further 30% of metabolism • The metabolites of lacosamide are not pharmacologically active • Autoinduction is not a feature of lacosamide metabolism Elimination: • The plasma half-life in healthy volunteers and in patients with epilepsy is 13 hours • Renal excretion: 40% of an administered dose is excreted unchanged in urine Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on lacosamide: –– To date, there have been no reports of AEDs affecting the clearance of lacosamide and affecting lacosamide plasma levels

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• Interactions between AEDs: effects by lacosamide: –– To date, there have been no reports of lacosamide affecting the clearance of AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on lacosamide: –– To date, there have been no reports of other non-AED drugs affecting the clearance of lacosamide and affecting lacosamide plasma levels • Interactions between AEDs and non-AED drugs:  effects by lacosamide: –– To date, there have been no reports of lacosamide affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • To date, none have been reported

Lacosamide

Hormonal contraception: • Lacosamide does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control Adverse effects How drug causes adverse effects: • Not known Common adverse effects: • Dizziness, headache, balance disorder, abnormal coordination, memory impairment, somnolence, tremor, nystagmus • Diplopia, blurred vision • Vertigo • Nausea, vomiting, constipation, flatulence • Pruritus • Depression Life-threatening or dangerous adverse effects: • Increases PR interval, therefore, patients with known second- or third-degree atrioventricular block may be at risk of myocardial infarction or heart failure • Particular caution should be exercised with the elderly as they may be at an increased risk of cardiac disorders and prescribed Class I antiarrhythmic drugs and also may be co-prescribed antiepileptic drugs (e.g., carbamazepine, lamotrigine, and pregabalin) that are known to be associated with PR prolongation

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Rare and not life-threatening adverse effects: • To date, none have been reported

the epilepsy prescriber’s guide to antiepileptic drugs Weight change: • No significant effect on weight is expected

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What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Risk of adverse effects is greatest in the first few months of treatment • Common adverse effects such as nausea often abate after a few months

Available formulations: • Tablets: 50 mg, 100 mg, 150 mg, 200 mg • Syrup (strawberry flavored): 15 mg/mL (200 mL/bottle and 465 mL/bottle) • Solution: 10 mg/mL (20 mL/vial)

Dosing and use

Dosing and use Usual dosage range: • Adults: 200–400 mg/day

How to dose: • When initiating lacosamide treatment start with a low dose and titrate slowly so as to minimize adverse effects –– For adults of age 16 years or older: start treatment with 50 mg twice daily for 1 week; increase by 100 mg/day in divided doses at weekly intervals; maximum dose 200 mg twice daily Dosing tips: • The solution for infusion and the tablets are bioequivalent and, therefore, can be used interchangeably • When using infusion, administer intravenously over 15–30 minutes twice daily How to withdraw drug: • There is no need to adjust dosage of concurrent medications as lacosamide is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Taper: reduce dose by 200 mg/week • Rapid discontinuation may increase the risk of seizures Overdose: • Following doses of 1200 mg/day dizziness and nausea are prevalent • In one case of lacosamide overdose (12 g) in conjunction with toxic doses of other antiepileptic drugs, the subject was initially comatose and then fully recovered without permanent sequelae

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• The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes ~50% of lacosamide from blood over 4 hours and, therefore, may be a useful procedure in cases of overdose

Lacosamide

Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests • Consider ECG to rule out atrioventricular block • During treatment: liver and kidney function tests every 12 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at lacosamide plasma concentrations of 10–20 mg/L (40–80 μmol/L) –– The conversion factor from mg/L to μmol/L is 3.99 (i.e., 1 mg/L = 3.99 μmol/L) –– The reference range of lacosamide in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Lacosamide can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant Other warnings/precautions: • Lacosamide can cause dizziness and blurred vision which could increase the occurrence of accidental injury or falls Do not use: • If patient has conduction problems or severe cardiac disease such as a history of myocardial infarction or heart failure • If a patient has a proven allergy to the active substance or to peanuts or soya or to any of its excipients • If a patient has hereditary problems of fructose intolerance (syrup formulation only) • If a patient suffers from phenylketonuria (syrup formulation only as it contains aspartame – a source of phenylalanine)

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Special populations Renal impairment: • Lacosamide and its metabolites are renally excreted • Mild to moderate renal impairment (CrCL >30 – <80 mL/min) results in increased lacosamide AUC values of ~30%; a dosage reduction may be necessary in some patients • Severe renal impairment (CrCL <30 mL/min) results in increased lacosamide AUC values of ~60%; a maximum dosage of 250 mg/ day is recommended for these patients • Because lacosamide can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of lacosamide

the epilepsy prescriber’s guide to antiepileptic drugs Hepatic impairment: • Lacosamide undergoes moderate metabolism (60%) in the liver and consequently lower doses may be required • Moderate hepatic impairment (Child-Pugh B) can be associated with a 20% increase in lacosamide AUC values

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Children: • Lacosamide is not licensed for use in children

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Lacosamide is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than lacosamide monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of lacosamide during pregnancy are not available Breast feeding • Breast milk:  it is not known whether lacosamide is excreted in breast milk • Breastfed infants: it is not known what plasma lacosamide concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

Special populations

Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in hepatic and renal function, lower lacosamide doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities, but the risk of pharmacokinetic interactions with lacosamide is low or nonexistent

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The overall place of lacosamide in the treatment of epilepsy Lacosamide has only recently been licensed for clinical use (2008). It is licensed for use as adjunctive treatment of partial-onset seizure (with or without secondary generalization) in patients with epilepsy aged 16 years and older. Because of its recent introduction, it is too early to ascertain the place of lacosamide in the treatment of patients with epilepsy. Primary seizure types: • Partial seizures with or without secondary generalization Secondary seizure types: • None Potential advantages: • Simple straightforward pharmacokinetics • Not associated with any significant pharmacokinetic interactions

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Potential disadvantages: • The adverse effect of vomiting may compromise compliance • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Ben-Menachem E, Biton V, Jatuzis D, Abdul-Khalil B, Doty P, Rudd GD. Efficacy and safety of oral lacosamide as adjunctive therapy in adults with partial-onset seizures. Epilepsia 2007; 48: 1308–1317. Beyreuther BK, Freitag J, Heers C, Krebsfanger N, Scharfenecker U, Stohr T. Lacosamide: a review of preclinical properties. CNS Drug Reviews 2007; 13: 21–42. Biton V, Rosenfeld WE, Whitesides J, Fountain NB, Vaiciene N, Rudd GD. Intravenous lacosamide as replacement of oral lacosamide in patients with partial-onset seizures. Epilepsia 2008; 49: 418–424. Doty P, Rudd D, Stoehr T, Thomas D. Lacosamide. Neurotherapeutics 2007; 4: 145–148. Halasz P, Kalviainen R, Mazurkiewicz-Beldzinska M, Rosenow F, Doty P, Hebert D, Sullivan T, on behalf of the SP755 Study Group. Adjunctive lacosamide for partial-onset seizures: efficacy and safety results from a randomized controlled study. Epilepsia 2009; 50: 443–453. Kellinghaus C, Berning S, Besselmann M. Intravenous lacosamide as successful treatment for nonconvulsive status epilepticus after failure of first-line therapy. Epilepsy & Behavior 2009; 14: 429–431.

the epilepsy prescriber’s guide to antiepileptic drugs

Lamotrigine Therapeutics Chemical name and structure: Lamotrigine, 3,5-diamino-6[2,3-dichlorophenyl]-1,2,4-triazine, is a white crystalline powder, with a molecular weight of 256.09 and an empirical formula of C9H7Cl 2N5.

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N N

Cl N

NH2

Brand names: • Elmendos • Labicitin; Labileno; Lamdra; Lamepil; Lamictal; Lamictin; Lamidus; Lamitrin; Lamitor; Lamodex; Lamogin; Lamogine; Lamotrix; Lamozine; Latrigine; Logem; Lotrigine • Mogine • Neurium • Plexxo; Protalgine • Seaze • Topepil

therapeutics

Cl H2N

Generics available: • Yes Licensed indications for epilepsy: • Monotherapy in adults and children over 12 years of age for the treatment of partial seizures and primary and secondarily generalized tonic–clonic seizures (UK-SPC; FDA-PI) • Adjunctive therapy in adults and children over 2 years of age and treatment of partial seizures and primary and secondarily generalized tonic–clonic seizures (UK-SPC; FDA-PI) • Adjunctive therapy in adults and children over 2 years of age of seizures associated with Lennox-Gastaut syndrome (UK-SPC; FDA-PI) Licensed indications for non-epilepsy conditions: • Maintenance treatment of bipolar I disorder (FDA-PI) Nonlicensed use for epilepsy: • Absence seizures

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Nonlicensed use for non-epilepsy conditions: • Bipolar depression • Bipolar II disorders • Cluster headaches • Depersonalization disorder • Migraine • Neuropathic pain • Peripheral neuropathy • Psychosis • Schizophrenia • Trigeminal neuralgia

Lamotrigine

Ineffective (contraindicated): • Lamotrigine is contraindicated for myoclonic jerks and syndromes with predominantly myoclonic jerks (e.g., juvenile myoclonic epilepsy, Dravet syndrome, and progressive myoclonic epilepsy) Mechanism of action: • Acts as a use-dependent blocker of voltage-sensitive sodium channels • Interacts with the open channel conformation of voltage-sensitive sodium channels • Interacts at a specific site of the alpha pore-forming subunit of voltage-sensitive sodium channels • Inhibits release of glutamate Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 2 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If lamotrigine is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: ≥95% • Food co-ingestion: causes a slight delay in the rate of absorption but the extent of absorption is unaffected • Tmax: 1–3 hours • Time to steady state: 3–7 days • Pharmacokinetics: linear • Protein binding: 55%

the epilepsy prescriber’s guide to antiepileptic drugs • Volume of distribution: 0.9–1.3 L/kg • Salivary concentrations:  lamotrigine is secreted into saliva and concentrations are similar to the unbound levels seen in plasma

Elimination: • In the absence of enzyme-inducing co-medication, half-life values for lamotrigine are 15–35 hours • In the absence of enzyme-inducing co-medication, but with valproic acid co-medication, half-life values for lamotrigine are 30–90 hours • In the presence of enzyme-inducing co-medication, half-life values for lamotrigine are 8–20 hours • In the presence of enzyme-inducing co-medication and also with valproic acid co-medication, half-life values for lamotrigine are 15–35 hours • Renal excretion:  ~90% of an administered dose is excreted as metabolites in urine; 2-N-glucuronide (76%), 5-N-glucuronide (10%), 2-N-methyl metabolite (0.14%), and other unidentified minor metabolites (4%) • Renal excretion:  approximately 10% of an administered dose is excreted as unchanged lamotrigine in urine

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on lamotrigine: –– Carbamazepine, methsuximide, oxcarbazepine, phenobarbital, phenytoin, and primidone can increase the clearance of lamo­ trigine and decrease lamotrigine plasma levels –– Valproic acid can decrease the clearance of lamotrigine and increase lamotrigine plasma levels • Interactions between AEDs: effects by lamotrigine: –– Lamotrigine can decrease plasma levels of clonazepam and valproic acid

Drug interaction profile

Metabolism: • Lamotrigine undergoes extensive metabolism in the liver, by conjugation with glucuronic acid, to various metabolites including 2-N-glucuronide (76% of dose) and 5-N-glucuronide (10% of dose), a 2-N-methyl metabolite (0.14% of dose) and other unidentified minor metabolites (4% of dose) • Glucuronidation is by means of UDP-glucuronosyltransferases and the isoform that is responsible for the N-glucuronidation of lamotrigine is UGT1A4 • The metabolites of lamotrigine are not pharmacologically active • Lamotrigine undergoes autoinduction so that clearance can incre­ ase by 17–37% and this may require an upward dosage adjustment when prescribed as monotherapy

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• Interactions between AEDs and non-AED drugs:  effects on lamotrigine: –– Oral contraceptives can increase the clearance of lamotrigine and decrease lamotrigine plasma levels –– Sertraline can increase lamotrigine plasma levels –– Acetaminophen, olanzapine, rifampicin, and ritonavir can decrease lamotrigine plasma levels • Interactions between AEDs and non-AED drugs:  effects by lamotrigine: –– To date, there have been no reports of lamotrigine affecting the clearance of other non-AED drugs and affecting their plasma levels

Lamotrigine

Pharmacodynamic drug interactions: • Concomitant administration with valproic acid is associated with a profound pharmacodynamic interaction whereby small doses of lamotrigine are associated with significant (synergistic) efficacy; adverse effects (e.g., disabling tremor) may also be exacerbated • Concomitant administration with carbamazepine has been associated with an increased risk of adverse effects (nausea, dizziness, headache, blurred vision, diplopia, and ataxia) • Concomitant administration with oxcarbazepine has been associated with an increased risk of adverse effects (nausea, dizziness, headache, blurred vision, diplopia, and ataxia) Hormonal contraception: • Lamotrigine does not enhance the metabolism of the estrogen (ethinylestradiol) component of hormonal contraceptives and, therefore, does not compromise contraception control • Lamotrigine can, however, enhance the metabolism of the progesterone (levonorgestrel) component of hormonal contraceptives and potentially lead to contraceptive failure when progesterone only contraceptive formulations are used; medium- or high-dose progesterone oral contraceptive preparations are advisable in patients taking lamotrigine

Adverse effects How drug causes adverse effects: • CNS adverse effects theoretically due to excessive actions at voltage-sensitive sodium channels • Rash hypothetically an allergic reaction

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Common adverse effects: • Benign rash (~10%) • Diplopia, dizziness, ataxia

the epilepsy prescriber’s guide to antiepileptic drugs • Headache • Tremor, asthenia, anxiety, drowsiness, insomnia • Nausea, vomiting, diarrhea

Adverse effects

Life-threatening or dangerous adverse effects: • Rare serious rash including Stevens-Johnson syndrome and toxic epidermal necrolysis (Lyell syndrome) can occur within 8 weeks of initiation of lamotrigine treatment or if medication is suddenly stopped then resumed at the normal dose–­ incidence in adults and children over 12 years old is 1 in 1000; incidence in children under 12 years old is from 1 in 300 to 1 in 100; risk of serious skin rash comparable to agents erroneously considered “safer” including carbamazepine, phenytoin, and phenobarbital • Risk of rash is increased in pediatric patients, especially in children under 12 and in children taking valproate • In children, the initial presentation of a rash can be mistaken for an infection; physicians should consider the possibility of a drug reaction if a child develops symptoms of rash and fever during the first 8 weeks of therapy • Rash can occur as part of a hypersensitive syndrome comprising a variable pattern of systemic symptoms including fever, lymphadenopathy, facial edema, and abnormalities of the blood and liver • Rare hematological abnormalities, which may not be necessarily associated with the hypersensitive syndrome, including neutropenia, leukopenia, anemia, thrombocytopenia, pancytopenia, and very rarely aplastic anemia and agranulocytosis • Rare hepatic dysfunction including hepatic failure • Lamotrigine, through its action in blocking cardiac rapid delayed rectifier potassium ion current, may increase the risk of cardiac arrhythmia and in turn sudden unexplained deaths in epilepsy (SUDEP)

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Rare and not life-threatening adverse effects: • Rare movement disorders such as tics have been reported • May exacerbate parkinsonian symptoms in patients with pre­existing Parkinson disease • Extrapyramidal effects and choreoathetosis may occur Weight change: • Not common; weight gain reported but not expected What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • If patient develops signs of a rash with benign characteristics (i.e., a rash that peaks within days, settles in 10–14 days, is spotty, nonconfluent, nontender, has no systemic features, and laboratory tests are normal):

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–– Reduce lamotrigine dose or stop dosage increase –– Warn patient to stop drug and contact physician if rash worsens or new symptoms emerge –– Prescribe antihistamine and/or topical corticosteroid for pruritus –– Monitor patient closely • If patient develops signs of a rash with serious characteristics (i.e., a rash that is confluent and widespread, or purpuric or tender; with any prominent involvement of neck or upper trunk; any involvement of eyes, lips, mouth, etc.; any associated fever, malaise, pharyngitis, anorexia, or lymphadenopathy; abnormal laboratory tests for complete blood count, liver function, urea, creatinine): –– Stop lamotrigine (and valproate if administered) –– Monitor and investigate organ involvement (hepatic, renal, hema­tological) –– Patient may require hospitalization

Lamotrigine

Dosing and use Usual dosage range: Dosage range varies depending on whether lamotrigine is prescribed as monotherapy, as a co-medicant with valproic acid or as a co-­ medicant with enzyme-inducing antiepileptic drugs. • For adults and children over 12 years: –– Monotherapy or adjunctive treatment with valproic acid: maintenance dose generally 100–200 mg/day given either as a single dose or in two equally divided doses; some patients have required 500 mg/day to achieve the desired response –– Adjunctive treatment with enzyme-inducing antiepileptic drugs: maintenance dose generally 200–400 mg/day given in two equally divided doses; some patients have required 700 mg/day to achieve the desired response • Children aged 2–12 years: –– Adjunctive treatment with valproic acid:  maintenance dose generally 1–5 mg/kg/day given either as a single dose or in 2 equally divided doses –– Adjunctive treatment with enzyme-inducing antiepileptic drugs: maintenance dose generally 5–15 mg/kg/day in two equally divided doses Available formulations: • Tablets: 25 mg, 50 mg, 100 mg, 200 mg • Dispersible chewable tablets: 2 mg, 5 mg, 25 mg, 100 mg

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How to dose: • Dosage and titration vary considerably depending on whether lamotrigine is prescribed as monotherapy, as a co-medicant with valproic acid or as a co-medicant with enzyme-inducing antiepileptic drugs

the epilepsy prescriber’s guide to antiepileptic drugs

Dosing tips: • Very slow dose titration may reduce the incidence of skin rash and risk of other adverse effects – thus dose should not be titrated faster than recommended • If patient stops taking lamotrigine for 5 days or more it may be necessary to restart the drug with the initial dose titration, as rashes have been reported on re-exposure • Advise patient to avoid new medications, foods, or products during the first 3 months of lamotrigine treatment to decrease the risk of unrelated rash; patients should also not start lamotrigine within 2 weeks of a viral infection, rash, or vaccination

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Dosing and use

• For adults and children over 12 years: –– Monotherapy: start treatment with 25 mg/day for 2 weeks; subsequently increase to 50 mg/day for 2 weeks; thereafter the dose should be increased by a maximum of 50–100 mg every 1–2 weeks until an optimum response is achieved; maintenance dose generally 100–200 mg/day given either as a single dose or in two equally divided doses –– Adjunctive treatment with valproic acid: start treatment with 25 mg every alternative day for 2 weeks; subsequently increase to 25 mg/day for 2 weeks; thereafter the dose should be increased by a maximum of 25–50 mg every 1–2 weeks until an optimum response is achieved; maintenance dose generally 200–400 mg/ day given either as a single dose or in two equally divided doses –– Adjunctive treatment with enzyme-inducing antiepileptic drugs:  start treatment with 50 mg/day for 2 weeks; subsequently increase to 100 mg/day for 2 weeks; thereafter the dose should be increased by a maximum of 100 mg every 1–2 weeks until an optimum response is achieved; maintenance dose generally 200–400 mg/ day given in two equally divided doses • Children aged 2–12 years: –– Adjunctive treatment with valproic acid:  start treatment with 0.15 mg/kg/day for 2 weeks; subsequently increase to 0.3 mg/kg/day for 2 weeks; thereafter the dose should be increased by a maximum of 0.3 mg/kg every 1–2 weeks until an optimum response is achieved; maintenance dose generally 1–5 mg/kg/day given either as a single dose or two equally divided doses; maximum dose generally 200 mg/day –– Adjunctive treatment with enzyme-inducing antiepileptic drugs:  start treatment with 0.6 mg/kg/day given in two equally divided doses for 2 weeks; subsequently increase to 1.2 mg/kg/day for 2 weeks; thereafter the dose should be increased by a maximum of 1.2 mg/kg every 1–2 weeks until an optimum response is achieved; maintenance dose generally 5–15 mg/kg/day given either as two equally divided doses; maximum dose generally 400 mg/day

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Lamotrigine

• If lamotrigine is added to patients taking valproate, remember that valproate inhibits lamotrigine metabolism and, therefore, titration rate and ultimate dose of lamotrigine should be reduced by 50% to reduce the risk of rash; conversely if concomitant valproate is discontinued after lamotrigine dose is stabilized, then the lamotrigine dose should be cautiously doubled over at least 2 weeks in equal increments each week following discontinuation of valproate • Also, if concomitant enzyme-inducing antiepileptic drugs (e.g., carbamazepine, phenobarbital, phenytoin and primidone) are discontinued after lamotrigine dose is stabilized, then the lamotrigine dose should be maintained for 1 week following discontinuation of the other drug and then reduced by half over 2 weeks in equal decrements each week • Dispersible chewable tablets should only be administered as whole tablets; dose should be rounded down to the nearest whole tablet; they can be dispersed by adding the tablet to liquid (enough to cover the drug); after approximately 1 minute the solution should be stirred and then consumed immediately in its entirety How to withdraw drug: • May need to adjust dosage of concurrent medications as lamo­ trigine is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper: a gradual dose reduction over a period of 2 weeks should be undertaken • Rapid discontinuation may induce withdrawal seizures and should only be undertaken if there are safety concerns (e.g., a rash with serious characteristics) Overdose: • Doses in excess of 10–20 times the maximum lamotrigine therapeutic dose have been ingested and some fatalities have occurred • Symptoms include ataxia, nystagmus, seizures, coma, and intraventricular conduction delay • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes lamotrigine from blood and, therefore, serves as a useful procedure in cases of overdose

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Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests • During treatment: liver and kidney function tests every 12 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at lamotrigine plasma concentrations of 3–15 mg/L (12–58 μmol/L)

the epilepsy prescriber’s guide to antiepileptic drugs –– The conversion factor from mg/L to μmol/L is 3.90 (i.e., 1 mg/L = 3.90 μmol/L) –– The reference range of lamotrigine in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Lamotrigine can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant

Special populations

Other warnings/precautions: • Life-threatening rashes have developed in association with lamo­ trigine use; lamotrigine should generally be discontinued at the first sign of serious rash • Risk of rash may be increased with higher doses, faster dose escalation, concomitant use of valproate, or in children under 12 years of age • Patient should be instructed to report any symptoms of hypersensitivity immediately (fever; flu-like symptoms; rash; blisters on skin or in eyes, mouth, ears, nose, or genital areas; swelling of eyelids, conjunctivitis, lymphadenopathy) • Caution is required when treating patients with a history of allergy or rash to other antiepileptic drugs – the frequency of nonserious rash after treatment with lamotrigine is three-fold greater • Depressive effects may be increased by other CNS depressants (e.g., alcohol, MAOIs, other antiepileptic drugs) • A small number of patients may experience a worsening of seizures • May cause photosensitivity • Lamotrigine binds to tissue that contains melanin, so for longterm treatment ophthalmologic checks may be considered • Lamotrigine inhibits dihydrofolate reductase and may, therefore, reduce folate concentrations

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Do not use: • If patient has a proven allergy to lamotrigine or to any of the exci­ pients

Special populations Renal impairment: • Lamotrigine is renally secreted and thus the dose may need to be lowered in renally impaired patients • Because lamotrigine can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of lamo­ trigine

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Hepatic impairment: • Lamotrigine is extensively metabolized and consequently lower doses will be required in patients with hepatic impairment • Dose may need to be reduced and titration may need to be slower, perhaps by 50% in patients with moderate impairment (ChildPugh grade B) and 75% in patients with severe impairment (ChildPugh grade C) Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

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Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in hepatic function, lower lamotrigine doses are appropriate • Because lamotrigine is associated with dizziness and ataxia the elderly are at increased risk of accidental injury (fall) • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with lamotrigine is substantial Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Lamotrigine is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than lamotrigine monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • During pregnancy lamotrigine pharmacokinetics change significantly so that lamotrigine plasma concentrations decrease by

the epilepsy prescriber’s guide to antiepileptic drugs 26–66% due to increased clearance consequent to enhanced glucuronidation; an increase in lamotrigine dose may be required in some patients

The overall place of lamotrigine in the treatment of epilepsy Lamotrigine is an effective broad-spectrum antiepileptic drug for the treatment of all types of seizures except myoclonic jerks. It is useful in the treatment of all focal or generalized, idiopathic or symptomatic epileptic syndromes of adults, children, and neonates. Although in monotherapy lamotrigine is less efficacious than carbamazepine in the management of focal seizures and primary generalized tonic– clonic seizures, it is better tolerated. In polytherapy, lamotrigine is particularly efficacious with valproate and this combination may be ideal for drug-resistant generalized epilepsies including those with myoclonic jerks. Usually, small doses of lamotrigine added to valproate may render previously intractable patients seizure-free.

Lamotrigine, overall role

Breast feeding • Breast milk: 40–80% of maternal plasma levels • Breastfed infants: lamotrigine plasma levels are 25–50% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (irritability or sedation) • If adverse effects are observed recommend bottle feed

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Primary seizure types: • Partial seizures • Generalized tonic–clonic seizures • Lennox-Gastaut syndrome Secondary seizure types: • Absence seizures Potential advantages: • Lamotrigine is a broad spectrum drug with significant efficacy • It is particularly efficacious with valproate as a result of pharmacodynamic synergism Potential disadvantages: • Associated with significant pharmacokinetic interactions with other antiepileptic drugs, which can be associated with exacerbation of adverse effects, requiring complex dosing and titration protocols • Very slow titration is required

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• Risk of a serious skin rash is a major consideration, particularly in patients receiving rapid lamotrigine titration and/or high dosing, in younger children and in those who are receiving concomitant valproate • Benign rashes related to lamotrigine may affect up to 10% of patients but resolve rapidly with drug discontinuation • Frequent dosage adjustments may be necessary before, during and after pregnancy and hormonal contraception • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Barr PA, Buettiker VE, Antony JH. Efficacy of lamotrigine in refractory neonatal seizures. Pediatric Neurology 1999; 20: 161–163. Barron TF, Hunt SL, Hoban TF, Price ML. Lamotrigine monotherapy in children. Pediatric Neurology 2000; 23: 160–163. Brodie MJ, Yuen AW. Lamotrigine substitution study: evidence for synergism with sodium valproate? 105 Study Group. Epilepsy Research 1997; 26: 423–432. Fitton A, Goa KL. Lamotrigine: an update of its pharmacology and therapeutic use in epilepsy. Drugs 1995; 50: 691–713. Frank LM, Enlow T, Holmes GL, Manesco P, Concannon S, Chen C, Womble G, Casale EJ. Lamictal (lamotrigine) monotherapy for typical absence seizures in children. Epilepsia 1999; 40: 973–979. Gamble C, Williamson PR, Chadwick DW, Marson AG. A metaanalysis of individual patient responses to lamotrigine or carbamazepine monotherapy. Neurology 2006; 66: 1310–1317. Glaucer TA, Cnaan A, Shinnar S, Hirtz DG, Dlugos D, Masur D, Clark PO, Capparelli EV, Adamson PC. For the Childhood Absence Epilepsy Study Group. Ethosuximide, valproic acid, and lamotrigine in childhood absence epilepsy. New England Journal of Medicine 2010; 362: 790–799. Guberman AH, Besag FM, Brodie MJ, Dooley JM, Duchowny MS, Pellock JM, Richens A, Stern RS, Trevathan E. Lamotrigineassociated rash:  risk/benefit considerations in adults and children. Epilepsia 1999; 40: 985–991. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. Marson AG, Al-Kharusi AM, Alwaid M, Appleton R, Baker GA, Chadwick DW, Cramp C, Cockerell OC, Cooper PN, Doughty J, Eaton B, Gamble C, Goulding PJ, Howell SJ, Hughes A, Jackson M, Jacoby A, Kellett M, Lawson GR, Leach JP, Nicolaides P, Roberts R, Shackley P, Shen J, Smith DF, Smith PE, Smith CT, Vanoli A,

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Lamotrigine, overall role

Williamson PR; SANAD Study Group. The SANAD study of effectiveness of carbamazepine, gabapentin, lamotrigine, oxcarbazepine, or topiramate for treatment of partial epilepsy: an unblinded ran­ domized controlled trial. Lancet 2007; 369: 1000–1015. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Patsalos PN, Berry DJ, Bourgeois BFD, Cloyd JC, Glauser TA, Johannessen SI, Leppik IE, Tomson T, Perucca E. Antiepileptic drugs  – Best practice guidelines for therapeutic drug monitoring: a position paper by the Subcommission on Therapeutic Drug Monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia 2008; 49: 1239–1276. Pennell PB, Newport DJ, Stowe ZN, Helmers SL, Montgomery JQ, Henry TR. The impact of pregnancy and childbirth on the metabolism of lamotrigine. Neurology 2004; 62: 292–295. Sabers A, Ohman I, Christensen J, Tomson T. Oral contraceptives reduce lamotrigine plasma levels. Neurology 2003; 61: 570–571. Tomson T, Luef G, Sabers A, Pittschieler S, Ohman I. Valproate effects on kinetics of lamotrigine in pregnancy and treatment with oral contraceptives. Neurology 2006; 67: 1297–1299. Zupanc ML. Antiepileptic drugs and hormonal contraceptives in adolescent women with epilepsy. Neurology 2006; 66(Suppl 3): S37–S45.

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Levetiracetam Therapeutics Chemical name and structure: Levetiracetam, (S)-alpha-ethyl-2 oxo-1-pyrrolidine acetamide, is a white to off-white crystalline powder, with a molecular weight of 170.21 and an empirical formula of C 8H14N2O2 .

O

N *

NH2

Levetiracetam

O Brand names: • Ceumid • Keppra; Keppra XR; Kopodex Generics available: • Yes Licensed indications for epilepsy: • Monotherapy of partial seizures with or without secondary generalization in patients aged 16 years and older (UK-SPC) • Adjunctive treatment of partial seizures with or without secondary generalization in adults and children from 4 years of age (UK-SPC) • Adjunctive treatment of myoclonic seizures in adults and adolescents from 12 years of age with juvenile myoclonic epilepsy (UK-SPC) • Adjunctive treatment of primary generalized tonic–clonic seizures in adults and adolescents from 12 years of age with idiopathic generalized epilepsy (UK-SPC) • Adjunctive treatment of partial onset seizures in patients 4 years and older (FDA-PI) • Adjunctive treatment of primary generalized tonic–clonic seizures in patients 6 years and older with idiopathic general epilepsies (FDA-PI) • Adjunctive treatment of myoclonic seizures in patients 12 years and older with juvenile myoclonic epilepsy (FDA-PI)

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Licensed indications for non-epilepsy conditions: • There are none

the epilepsy prescriber’s guide to antiepileptic drugs Nonlicensed use for epilepsy: • Absence seizures • Benign rolandic epilepsy • Juvenile myoclonic epilepsy • Myoclonic seizures • Myoclonus (post-hypoxic and post-encephalitic) • Neuropathic pain/chronic pain • Progressive myoclonic epilepsy (Unverricht-Lundborg syndrome) • Severe myoclonic epilepsy in infancy (Dravet syndrome) • Status epilepticus

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Nonlicensed use for non-epilepsy conditions: • Mania

Mechanism of action: • The precise mechanism by which levetiracetam exerts its antiepileptic activity is unknown • Levetiracetam does not share with other antiepileptic drugs any of their three main mechanisms, such as sodium channel blockade, inhibition of calcium currents, or increase in GABAergic inhibitory responses • Levetiracetam can oppose the activity of negative modulators of GABA- and glycine-gated currents, and can partially inhibit N-type calcium currents • Binds to synaptic vesicle protein SV2A, which is involved in synaptic vesicle exocytosis Efficacy profile: • The goal of treatment is complete remission of seizures • Onset of efficacy occurs mostly within the first 2 weeks of treatment • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • Levetiracetam can suppress interictal epileptiform activity in certain forms of epilepsy • Levetiracetam appears to be as effective as carbamazepine against partial seizures • Levetiracetam can be effective in all types of primary (or idiopathic) generalized epilepsies

Therapeutics

Ineffective (contraindicated): • Levetiracetam is potentially effective against all seizure types and is not contraindicated for any seizure type or epilepsy • Experience in neonatal seizures is very limited • There is no information regarding its effectiveness for prophylaxis of febrile seizures

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• If levetiracetam is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Levetiracetam

Pharmacokinetics Absorption and distribution: • Oral bioavailability: ≥95% • Food co-ingestion: causes a slight delay in the rate of absorption but the extent of absorption is unaffected • Tmax: 1–2 hours • Time to steady state: 1–2 days • Pharmacokinetics: linear • Protein binding: 0% • Volume of distribution: 0.5–0.7 L/kg • Salivary concentrations:  levetiracetam is secreted into saliva and concentrations are similar to the unbound levels seen in plasma Metabolism: • Levetiracetam undergoes minimal metabolism with ~30% of the dose metabolized by hydrolysis to a deaminated metabolite • This metabolism is independent of the hepatic cytochrome P450 system and is by means of a type-B esterase enzyme located in whole blood • The metabolites of levetiracetam are not pharmacologically active • Autoinduction is not a feature of levetiracetam metabolism Elimination: • The elimination half-life of levetiracetam is 6–8 hours in adults, 5–6 hours in children, and 10–11 hours in the elderly • The renal clearance of levetiracetam is proportional to the creatinine clearance • Renal excretion:  ~66% of an administered dose is excreted unchanged in urine

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Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on levetiracetam: –– To date, there have been no reports of AEDs affecting the clearance of levetiracetam and affecting levetiracetam plasma levels • Interactions between AEDs: effects by levetiracetam: –– To date, there have been no reports of levetiracetam affecting the clearance of other AEDs and affecting their plasma levels

the epilepsy prescriber’s guide to antiepileptic drugs • Interactions between AEDs and non-AED drugs: effects on leve­ tiracetam: –– To date, there have been no reports of other non-AED drugs affecting the clearance of levetiracetam and affecting levetiracetam plasma levels • Interactions between AEDs and non-AED drugs: effects by levetiracetam: –– To date, there have been no reports of levetiracetam affecting the clearance of other non-AED drugs and affecting their plasma levels

Hormonal contraception: • Levetiracetam does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects

Pharmacodynamic drug interactions: • An encephalopathic state induced by the addition of levetiracetam to valproate has been described • Disabling symptoms compatible with carbamazepine toxicity were reported in patients in whom levetiracetam was added to carbamazepine • Topiramate-related adverse effects were exacerbated in children co-prescribed with levetiracetam • Other central nervous depressants, such as alcohol, other antiepileptic drugs, and MAO inhibitors may exacerbate the depressive effect of levetiracetam

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Adverse effects How drug causes adverse effects: • Mechanism by which levetiracetam causes adverse effects has not been established • CNS adverse effects may be due to excessive actions on SV2A synaptic vesicle proteins or to actions on various voltage-sensitive ion channels Common adverse effects: • Somnolence, asthenia, ataxia, dizziness • Behavioral symptoms (particularly common in children), including agitation, hostility, oppositional behavior, anxiety, aggression, emotional lability, depression Life-threatening or dangerous adverse effects: • Very rare liver failure • Rare activation of suicidal ideation and acts Rare and not life-threatening adverse effects: • Psychosis

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• Allergic reaction • Bone marrow suppression Weight change: • Not common; weight gain reported but not expected

Levetiracetam

What to do about adverse effects: • Discuss common adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Risk of adverse effects is greatest in the first few months of treatment • Slower titration may decrease incidence or severity of some adverse effects • Administration of pyridoxine (vitamin B6) has been suggested to reduce behavioral adverse reactions in children, but this has not yet been supported by controlled data • Negative effect of levetiracetam on behavior and mood often persists and may require discontinuation of levetiracetam

Dosing and use Usual dosage range: • Adults: 1000–3000 mg/day • Children: 30–40 mg/kg/day Available formulations: • Tablets: 250 mg, 500 mg, 750 mg, 1000 mg • Oral solution: 100 mg/mL, 500 mg/5 mL • Solution for intravenous injection: 100 mg/mL, 500 mg/5 mL • Extended-release tablets: 500 mg How to dose: • For adults and children over 12 years of age: start treatment with 250– 500 mg twice daily; at intervals of 1–2 weeks increase as needed and as tolerated by 500 mg/day; maintenance dose generally 2000–3000 mg/day; some patients may tolerate and respond to doses greater than 3000 mg/day • Children under 12 years of age: start treatment with approximately 20 mg/kg/day, twice daily or 3 times daily; at intervals of 1–2 weeks increase as needed and as tolerated by approximately 10–20 mg/kg/day; maintenance dose generally 30–40 mg/kg/day; doses of up to 100 mg/kg/day may be necessary and well tolerated, especially in younger children

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Dosing tips: • Slower titration may decrease incidence or severity of some adverse effects

the epilepsy prescriber’s guide to antiepileptic drugs • In children, and at high doses, the daily dose may be preferably divided into three doses • A dose for intravenous loading has not been determined, but 20–40 mg/kg have been administered safely to children with acute repetitive seizures or status epilepticus • Intravenous doses can be infused diluted in 100 mL of isotonic fluids (e.g., normal saline, lactated Ringer’s, 5% dextrose) over 15 minutes • For intolerable sedation, can give most of the dose at night and less during the day

Overdose: • No fatalities have been reported: symptoms include sedation, ­a gitation, aggression, respiratory depression, coma • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes levetiracetam from blood and, therefore, serves as a useful procedure in cases of overdose

Dosing and use

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as levetiracetam is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • No data are available on potential for withdrawal seizures or symptoms upon rapid discontinuation • Rapid discontinuation may increase the risk of seizures • If possible, taper dose over a period of 1–3 months

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Tests and therapeutic drug monitoring: • There is no need to monitor any laboratory parameter during treatment with levetiracetam • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at levetiracetam plasma concentrations of 12–46 mg/L (70–270 μmol/L) –– The conversion factor from mg/L to μmol/L is 5.88 (i.e., 1 mg/L = 5.88 μmol/L) –– The reference range of levetiracetam in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Levetiracetam can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant Other warnings/precautions: • Patients should be monitored carefully for signs of depression or psychosis

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Do not use: • In patients with a history of allergic reaction to levetiracetam • Because malitol is an excipient of levetiracetam, patients with rare hereditary problems of fructose intolerance should not take this medication

Levetiracetam

Special populations Renal impairment: • Renal disease may decrease levetiracetam clearance by 35–60% • Levetiracetam dosage should be individualized according to creatinine clearance –– Recommended dose for patients with mild impairment (CrCL 50–79 mL/min/1.73 m 2) is 500–1000 mg twice a day –– Recommended dose for patients with moderate impairment (CrCL 30–49 mL/min/1.73 m 2) is 250–750 mg twice a day –– Recommended dose for patients with severe impairment (CrCL <30 mL/min/1.73 m 2) is 250–500 mg twice a day • Because levetiracetam can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of levetiracetam; typically 500–1000 mg once a day will be required followed with a supplemental dose of 250–500 mg following dialysis Hepatic impairment: • Levetiracetam is not metabolized in the liver and, therefore, no dosage adjustment is necessary Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma level Elderly: • Elderly patients are more susceptible to adverse effects (especially somnolence) and, therefore, often do better at lower doses • Because of an age-related reduction in renal function, lower levetiracetam doses are appropriate and dosage may need to be guided by creatinine clearance • Invariably the elderly are prescribed drug therapies for concurrent comorbidities, but the risk of pharmacokinetic interactions with levetiracetam is low or nonexistent • Considering also the relatively safe profile of levetiracetam, it may be a first-choice antiepileptic drug in the elderly

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Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all

the epilepsy prescriber’s guide to antiepileptic drugs

Breast feeding • Breast milk: 80–130% of maternal plasma levels • Breastfed infants: levetiracetam plasma levels are <20% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (irritability or sedation) • If adverse effects are observed recommend bottle feed

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Levetiracetam, overall role

antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Levetiracetam is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than levetiracetam monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • During pregnancy levetiracetam pharmacokinetics change significantly so that levetiracetam plasma concentrations decrease by ~60% due to increased clearance; an increase in levetiracetam dose may be required in some patients

The overall place of levetiracetam in the treatment of epilepsy Levetiracetam is a broad spectrum antiepileptic drug and represents a first line or second line therapy in idiopathic generalized epilepsies (generalized and myoclonic seizures) and in partial seizures with or without secondary generalization where it is the main challenger for carbamazepine. It is also a likely candidate to replace valproate in the treatment of juvenile myoclonic epilepsy and of idiopathic generalized epilepsies in general. Because levetiracetam is associated with a relatively good safety profile, does not cause significant idiosyncratic reactions, has simple pharmacokinetic characteristics and has a low propensity to interact with other medications makes its clinical use straightforward and uncomplicated. Primary seizure types: • Partial seizures with or without secondary generalization • Myoclonic seizures associated with juvenile myoclonic epilepsy

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• Primary generalized tonic–clonic seizures associated with idio­ pathic generalized epilepsy Secondary seizure types: • Absence seizures • Progressive myoclonic epilepsy • Severe myoclonic epilepsy of infancy (Dravet syndrome) • Myoclonus Potential advantages: • Broad spectrum of seizure protection • Has no organ toxicity (i.e., liver, kidneys, bone marrow, etc.) and has virtually no dangerous or life-threatening adverse effects • Simple straightforward pharmacokinetics • Not associated with any significant pharmacokinetic interactions

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Potential disadvantages: • Behavioral and mood alterations are relatively common, especially in children, and may necessitate discontinuation • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Ben-Menachem E, Falter U; for the European Levetiracetam Study Group. Efficacy and tolerability of levetiracetam 3000 mg/d in patients with refractory partial seizures:  a multicenter, doubleblind, responder-selected study evaluating monotherapy. Epilepsia 2000; 41: 1276–1283. Berkovic SF, Knowlton RC, Leroy RF, Schiemann J, Falter U; Levetiracetam N01057 Study Group. Placebo-controlled study of levetiracetam in idiopathic generalized epilepsy. Neurology 2007; 69: 1751–1760. Brodie MJ, Perucca E, Ryvlin P, Ben-Menachem E, Meencke HJ; Levetiracetam Monotherapy Study Group. Comparison of levetiracetam and controlled-release carbamazepine in newly diagnosed epilepsy. Neurology 2007; 68: 402–408. Gallagher MJ, Eisenman LN, Brown KM, Erbayat-Altay E, Hecimovic H, Fessler AJ, Attarian HP, Gilliam FG. Levetiracetam reduces spike-wave density and duration during continuous EEG monitoring in patients with idiopathic generalized epilepsy. Epilepsia 2004; 45: 90–91. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. Kossoff EH, Bergey GK, Freeman JM, Vining EP. Levetiracetam psychosis in children with epilepsy. Epilepsia 2001; 42: 1611–1613.

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Levetiracetam, overall role

Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Patsalos PN. Pharmacokinetic profile of levetiracetam: toward ideal characteristics. Pharmacology and Therapeutics 2000; 85: 77–85. Patsalos PN. Clinical pharmacokinetics of levetiracetam. Clinical Pharmacokinetics 2004; 43: 707–724. Patsalos PN. Levetiracetam:  pharmacology and therapeutics in the treatment of epilepsy and other neurological conditions. Reviews in Contemporary Pharmacotherapy 2004; 13: 1–168. Patsalos PN, Ghattura S, Ratnaraj N, Sander JW. In situ metabolism of levetiracetam in blood of patients with epilepsy. Epilepsia 2006; 47: 1818–1821. Pellock JM, Glauser TA, Bebin EM, Fountain NB, Ritter FJ, Coupez RM, Shileds WD. Pharmacokinetic study of levetiracetam in children. Epilepsia 2001; 42: 1574–1579. Rocamora R, Wagner K, Schulze-Bonhage A. Levetiracetam reduces frequency and duration of epileptic activity in patients with refractory primary generalized epilepsy. Seizure 2006; 15: 428–433. Shorvon SD, Löwenthal A, Janz D, Bielen E, Loiseau P; for the European Levetiracetam Study Group. Multicenter doubleblind, randomized, placebo-controlled trial of levetiracetam as add-on therapy in patients with refractory partial seizures. Epilepsia 2000; 41: 1179–1186. Specchio LM, Gambardella A, Giallonardo AT, Michelucci R, Specchio N, Boero G, La Neve A. Open label, long-term, pragmatic study on levetiracetam in the treatment of juvenile myoclonic epilepsy. Epilepsy Research 2006; 71: 32–39.

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Lorazepam Therapeutics Chemical name and structure: Lorazepam,   7-chloro-5-(2-chlorophenyl)–1,3-dihydro-3-dihy­ droxy-2H-1,4-benzodiazepine-2-one, is a nearly white crystalline substance, with a molecular weight of 321.16 and an empirical formula of C15H10CI 2N2O2 . H O

N

OH Cl

N

Lorazepam

CI

Brand names: • Abinol; Ansilor; Anxira; Anzepam; Aplacasse; Aripax; Ativan • Bonatranquan • Control • Emoten; Emotival • Larpose; Laubeel; Lauracalm; Lonza; Lopam; Lora; Lorabenz; Lorafen; Loram; Lorans; Lorapam; Lorax; Lorazene; Lorazep; Loraxepam-Efeka; Lorazepam-Eurogenerics; Lorazin; Lorazon; Lorenin; Loridem; Lorivan; Lorsilan; Lorzem • Merlit; Merlopam • Nervistop L; Neuropam; Novhepar, Nu-Loraz • Orfidal • Psicopax • Renaquil • Sedatival; Sidenar; Silence; Stapam • Tavor; Temesta; Titus; Tranqipam; Trapax; Trapex • Vigiten • Zora Generics available: • Yes

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Licensed indications for epilepsy: • Status epilepticus (UK-SPC; FDA-PI)

the epilepsy prescriber’s guide to antiepileptic drugs Licensed indications for non-epilepsy conditions: • Anxiety disorder (UK-SPC; FDA-PI) • Anxiety associated with depressive symptoms (FDA-PI) • Insomnia (UK-SPC) • Sedation with amnesia (peri-operative) (UK-SPC)

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Nonlicensed use for epilepsy: • Myoclonic seizures • Neonatal seizures

Ineffective (contraindicated): • Lorazepam is potentially effective against all types of seizures and is not contraindicated for any form of epilepsy • Lorazepam may cause tonic seizures in patients with epileptic encephalopathies being treated for atypical absence status epilepticus

Therapeutics

Nonlicensed use for non-epilepsy conditions: • Acute mania (adjunctive) • Acute psychosis (adjunctive) • Alcohol withdrawal psychosis • Headache • Muscle spasm • Panic disorder • Post-anoxic myoclonus

Mechanism of action: • Benzodiazepines bind to the neuronal GABA A receptor, a ligandgated chloride channel • Benzodiazepines do not act directly on the chloride channel, but enhance binding of GABA to the receptor • When GABA binds to the GABA A receptor, it increases the frequency, but not the duration, of the opening of the chloride ion channel, which results in hyperpolarization of the membrane and reduction in neuronal firing • Activation of the chloride channel enhances inhibitory neuro­ transmission • Benzodiazepines also influence sodium channel function at high concentrations Efficacy profile: • The goal of treatment is complete remission of seizures • The onset of action is very rapid, particularly after intravenous administration • For the treatment of status epilepticus, the administration of lorazepam is usually followed by a bolus of phenytoin or fosphenytoin,

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particularly if there is no cessation of status after the lorazepam dose • Like other benzodiazepines, lorazepam often loses its efficacy during chronic use

Lorazepam

Pharmacokinetics Absorption and distribution: • First pass hepatic transformation decreases the absolute systemic availability of oral lorazepam to 29% of that following intravenous administration • When lorazepam is administered orally, peak plasma levels are achieved within 1.5–2 hours • Lorazepam is absorbed more rapidly when administered sublingually than orally or intramuscularly and peak plasma levels are achieved within 1 hour • Lorazepam entry into the brain is rapid, but probably slower than the brain penetration of diazepam • Whereas intravenous bolus injection produces high brain levels rapidly, it is noteworthy that within 2 hours of administration, similar blood levels are produced by intravenous and intramuscular injection or oral administration – thus any of these routes will suffice for nonurgent therapy (e.g., in partial status) • When lorazepam parenteral solution is administered rectally, absorption is slow; peak concentrations are lower than those achieved following intravenous administration, and may not be reached for 1–2 hours • Pharmacokinetics: linear • Volume of distribution: 1.0–2.0 L/kg • Protein binding: 90% • Salivary concentrations:  it is not known whether lorazepam is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma Metabolism: • Lorazepam is metabolized rapidly in the liver by glucuronidation at the 3-hydroxy position • Approximately 75% of the lorazepam dose is excreted by the kidneys as glucuronide • The glucuronide metabolite is not pharmacologically active • Autoinduction is not a feature of lorazepam metabolism

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Elimination: • In adults the elimination half-life values for lorazepam are 8–24 hours

the epilepsy prescriber’s guide to antiepileptic drugs • In children the elimination half-life values for lorazepam are 7.6–13.4 hours • In neonates half-life values are ~40 hours • Renal excretion:  <1% of an administered dose is excreted unchanged in urine

drug interaction profile

Drug interaction profile Pharmacokinetic drug interactions: There have been no formal studies of interactions with lorazepam but there is a significant likelihood of interaction with some drugs (e.g., lamotrigine, oxcarbazepine, valproic acid) consequent to the mode of metabolism (glucuronidation) of lorazepam. • Interactions between AEDs: effects on lorazepam: –– Carbamazepine, phenobarbital, phenytoin, and primidone can increase the clearance of lorazepam and decrease lorazepam plasma levels –– Valproate can decrease the clearance of lorazepam and increase lorazepam plasma levels • Interactions between AEDs: effects by lorazepam: –– To date, there have been no reports of lorazepam affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on lorazepam: –– Oral contraceptives may increase the clearance of lorazepam and decrease plasma lorazepam levels –– Probenecid can decrease the clearance of lorazepam and increase lorazepam plasma levels • Interactions between AEDs and non-AED drugs:  effects by lorazepam: –– To date, there have been no reports of lorazepam affecting the clearance of other non-AED drugs and affecting their plasma levels

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Pharmacodynamic drug interactions: • Patients receiving long-term therapy with other benzodiazepines are less responsive to lorazepam in status epilepticus • The cardiovascular and respiratory depression by lorazepam can be exacerbated by co-medication with phenobarbital • Lorazepam potentiates the action of CNS depressant drugs Hormonal contraception: • Lorazepam does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

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Adverse effects How drug causes adverse effects: • Mechanism by which lorazepam causes adverse effects is probably the same as for seizure protection:  enhancement of inhibitory neurotransmission through activation of the chloride ion channel • Long-term adaptations in benzodiazepine receptors may explain the development of dependence, tolerance, and withdrawal • Adverse effects are generally immediate, but often disappear in time

Lorazepam

Common adverse effects: • Sedation, drowsiness, fatigue • Nausea • Ataxia, dizziness, slurred speech, weakness • Psychomotor slowing • Cognitive dysfunction, forgetfulness, confusion • Respiratory depression • Hypotension • Paradoxical reactions including agitation, restlessness and hyper­ activity • Hypersecretion and drooling (hypersalivation), dry mouth • Pain at injection site Life-threatening or dangerous adverse effects: • Other than respiratory depression, lorazepam has no life-threatening or dangerous adverse effects • Hypersensitivity reactions are very rare • Rare hepatic dysfunction, renal dysfunction, blood dyscrasias Rare and not life-threatening adverse effects: • Rare hallucinations • Mania Weight change: • Not common; weight gain reported but not expected

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What to do about adverse effects: • Because lorazepam is most commonly used in emergency situations, the only adverse effect that is of major relevance is respiratory depression • All patients given more than 0.5–1.0 mg/kg of lorazepam should be monitored carefully for respiratory depression; adequate supportive equipment should be readily available • Because of the development of tolerance associated with benzodiazepine therapy, starting at a low dose in nonurgent cases will usually decrease the incidence or severity of CNS adverse effects

the epilepsy prescriber’s guide to antiepileptic drugs • In patients treated with maintenance doses of lorazepam, some CNS-related adverse effects may be lessened by slow titration, but they may persist at low doses despite slow titration

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Dosing and use Usual dosage range: • Intravenous dose: 0.1 mg/kg, maintenance doses of 0.5–1.0 mg/kg (maximum dose 4 mg) • Oral sublingual dose:  0.05–0.15 mg/kg, maintenance doses of 0.5–1.0 mg/kg (maximum dose 4 mg) • Patients can be maintained on oral or intravenous maintenance doses of 0.5–1.0 mg/kg (maximum 4 mg) every 6–8 hours

How to dose: • The recommended intravenous dose of lorazepam is 0.1 mg/kg (maximum dose 4 mg); this dose may be repeated if necessary after 10 minutes and administration should not exceed 2 mg/min • The recommended sublingual dose is 0.05–0.15 mg/kg (maximum 4 mg) • Patients can be maintained on oral or intravenous maintenance doses of 0.5–1.0 mg/kg (maximum 4 mg) every 6–8 hours

Dosing and use

Available formulations: • Tablets: 0.5 mg, 1.0 mg, 2.0 mg, 2.5 mg • Parenteral solution:  2 mg/mL (1 and 10 mL ampule), 4 mg/mL (1 and 10 mL ampule)

Dosing tips: • Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating effects • Take liquid formulation with water, soda, apple sauce, or pudding • Injectable lorazepam is intended for acute use; patients who require long-term treatment should be switched to the oral formulation • Use lowest possible effective dose for the shortest possible period of time • Assess need for continuous treatment regularly • Risk of dependence may increase with dose and duration of treatment • Frequency of dosing in practice is often greater than predicted from half-life, as duration of biological activity is often shorter than pharmacokinetic terminal half-life How to withdraw drug: • There is no need to adjust dosage of concurrent medications as lorazepam is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section)

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• Abrupt discontinuation of lorazepam has been associated with withdrawal seizures, which may occur up to 60 hours following its discontinuation • After acute or sub-acute treatment with repeated doses, the dose should be tapered down over 2–3 days • In cases of chronic use, taper dose over a period of 1–2 months • Taper by 0.5 mg every 3 days to reduce chances of withdrawal effects • For difficult to taper cases, consider reducing dose much more slowly after reaching 3 mg/day, perhaps by as little as 0.25 mg per week or less • For other patients with severe problems discontinuing a benzodiazepine, dosing may need to be tapered over many months (i.e., reduce dose by 1% every 3 days by crushing tablet and suspending or dissolving in 100 mL of fruit juice and then disposing of 1 mL while drinking the rest; 3–7 days later, dispose of 2 mL, and so on). This is both a form of very slow biological tapering and a form of behavioral desensitization

Lorazepam

Overdose: • Fatalities can occur: symptoms include severe respiratory depression, hypotension, tiredness, ataxia, confusion, coma • Lorazepam overdoses have also been found to cause specifically hallucinations, delirium and transient global amnesia • Treatment of overdoses consists of supportive care and the administration of the benzodiazepine receptor antagonist flumazenil. Aminophylline has also been used • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis does not remove lorazepam from blood and, therefore, does not serve as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • There is no need to monitor any laboratory parameter during treatment with lorazepam • Therapeutic drug monitoring: uncommon –– Optimum seizure control in patients on monotherapy is most likely to occur at plasma lorazepam concentrations of 20–30 μg/L (60–90 nanomol/L) –– The conversion factor from μg/L to nanomol/L is 3.11 (i.e., 1 μg/L = 3.11 nanomol/L) –– The reference range of lorazepam in plasma is considered to be the same for children and adults although no data are available to support this clinical practice

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Other warnings/precautions: • Patients should be monitored carefully for evidence of respiratory depression, accumulation of secretions and impairment of swallowing

the epilepsy prescriber’s guide to antiepileptic drugs

Do not use: • Use with caution in patients with a history of paradoxical or psychotic reaction to lorazepam, or to other benzodiazepines • In patients that have narrow angle-closure glaucoma • In patients that have sleep apnea (injection) • If there is a proven allergy to lorazepam or any other benzo­d iazepine

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Special populations

• Lorazepam is a Schedule IV drug and the risk of dependence may increase with dose and duration of treatment • Patients may develop dependence and/or tolerance with longterm use • Use with caution in patients with pulmonary disease; rare reports of death after initiation of benzodiazepines in patients with severe pulmonary impairment • History of drug or alcohol abuse often creates greater risk for dependency • Use oral formulation only with extreme caution if patient has obstructive sleep apnea; injection is contraindicated in patients with sleep apnea • Some depressed patients may experience a worsening of suicidal ideation • Some patients may exhibit abnormal thinking or behavioral changes similar to those caused by other CNS depressants (i.e., either depressant actions or disinhibiting actions) • Lorazepam must not be administered intra-arterially because it may cause arteriospasm and result in gangrene

Special populations Renal impairment: • Renal failure does not require a reduction in lorazepam dosage Hepatic impairment: • Severe hepatic failure may prolong the half-life of lorazepam and may lower protein binding • Because of its short half-life and inactive metabolites, lorazepam may be a preferred benzodiazepine in some patients with liver disease Children: • Children do not require additional precautions or monitoring Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, often do better at lower doses • Protein binding of lorazepam is slightly lower in the elderly • A mean 20% reduction in total body clearance of lorazepam has been reported

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Lorazepam

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Lorazepam is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy, especially of seizure disorders] • Infants whose mothers received a benzodiazepine late in pregnancy may experience withdrawal effects • Neonatal flaccidity has been reported in infants whose mothers took a benzodiazepine during pregnancy • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than lorazepam monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • It is not known whether during pregnancy lorazepam pharmacokinetics change, necessitating the need to undertake a dosage adjustment Breast feeding • Breast milk:  transfer of lorazepam into breast milk is minimal because of extensive binding to serum proteins • Breastfed infants: it is not known what plasma lorazepam concentrations are achieved in breastfed infants compared with the levels of their mothers • Lorazepam is virtually never used as an antiepileptic drug for a sufficiently long time to have an impact on breast feeding • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (feeding difficulties, sedation, and weight loss) • If adverse effects are observed recommend bottle feed

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The overall place of lorazepam in the treatment of epilepsy As is the case with some other benzodiazepines, lorazepam use in the treatment of epilepsy is largely limited to acute and sub-acute situations and is usually the drug of first choice in the treatment of status epilepticus. It has a high affinity for the benzodiazepine receptor so that its antiepileptic efficacy is similar to that of clonazepam. A very important potential advantage of lorazepam over diazepam is its longer duration of action, in both adults and children, and in neonates, where effects lasting 12 hours or more are usual.

the epilepsy prescriber’s guide to antiepileptic drugs Primary seizure types: • Emergency treatment of status epilepticus

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Secondary seizure types: • Acute repetitive seizures • Neonatal seizures • Myoclonic seizures • Post-anoxic myoclonus

Lorazepam, overall role

Potential advantages: • Rapid onset of action and availability in a variety of formulations (oral liquids as well as injectable formulations) • Single injection produces a long-lasting effect • Intravenous lorazepam is more effective than intravenous diazepam in the treatment of status epilepticus • Compared with diazepam, intravenous lorazepam has fewer adverse effects and a longer duration of action • Sublingual lorazepam is a convenient and effective treatment of serial seizures in children • Lorazepam has virtually no organ toxicity and has a low risk of hypotension • Lorazepam may be preferred over other benzodiazepines for patients with liver or renal disease because its pharmacokinetics are unaffected in such patients Potential disadvantages: • The effectiveness of lorazepam in the chronic treatment of epilepsy is limited by its sedative and behavioral effects and by the development of tolerance to the protective effect against seizures • Lorazepam may exacerbate or cause tonic seizures • Abrupt discontinuation of lorazepam, and benzodiazepines in general, can lead to withdrawal seizures and withdrawal symptoms • Potential teratogen, but not more than most other antiepileptic drugs Suggested reading Appleton R, Sweeney A, Choonara I, Robson J, Molyneux E. Lorazepam versus diazepam in the acute treatment of epileptic seizures and status epilepticus. Developmental Medicine and Child Neurology 1995; 37: 682–688. DiMario FJ Jr, Clancy RR. Paradoxical precipitation of tonic seizures by lorazepam in a child with atypical absence seizures. Pediatric Neurology 1988; 4: 249–251. Greenblatt DJ, Ehrenberg BL, Gunderman J, Scavone JM, Tai NT, Harmatz JS, Shader RI. Kinetic and dynamic study of intravenous lorazepam: comparison with intravenous diazepam. Journal of Pharmacology and Experimental Therapeutics 1989; 250: 134–140.

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McDermott CA, Kowalczyk AL, Schnitzler ER, Mangurten HH, Rodvold KA, Metrick S. Pharmacokinetics of lorazepam in critically ill neonates with seizures. Journal of Pediatrics 1992; 120: 479–483. Prasad K, Al-Roomi K, Krishnan PR, Sequeira R. Anticonvulsant therapy for status epilepticus. Cochrane Database Systematic Reviews 2005; 4: CD003723. Relling MV, Mulhern RK, Dodge RK, Johnson D, Pieper JA, Rivera GK, Evans WE. Lorazepam pharmacodynamics and pharmacokinetics in children. Journal of Pediatrics 1989; 114: 641–646. Riviello JJ Jr, Holmes GL. The treatment of status epilepticus. Seminars in Pediatric Neurology 2004; 11: 129–138.

the epilepsy prescriber’s guide to antiepileptic drugs

Methsuximide Therapeutics Chemical name and structure: Methsuximide, N-2-dimethyl-2-phenyl-succinimide, is a white powder, with a molecular weight of 203.23 and an empirical formula of C12H13NO2 .

M

CH3

O

N CH3

O

Generics available: • No

therapeutics

Brand names: • Celontin • Petinutin

Licensed indications for epilepsy: • Absence seizures that are refractory to other antiepileptic drugs (FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • Partial seizures • Myoclonic seizures • Astatic seizures (drop attacks) Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Generalized tonic–clonic seizures Mechanism of action: • Not established Efficacy profile: • The goal of treatment is complete remission of seizures • Onset of action may occur within the first few days

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• Goal of therapy in typical absence seizures is not only full seizure control, but also normalization of EEG • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • If partially effective, consider co-prescribing with lamotrigine or valproic acid, or switch to valproic acid, lamotrigine, levetiracetam, acetazolamide, topiramate, or zonisamide

Methsuximide

Pharmacokinetics Absorption and distribution: • Oral bioavailability: not established • Food co-ingestion:  it is not known whether food co-ingestion affects the rate or extent of absorption • Tmax:  1–4 hours (for pharmacologically active metabolite N-desmethylmethsuximide) • Time to steady state: 8–16 days • Pharmacokinetics: linear • Protein binding: 45–60% (for N-desmethylmethsuximide) • Volume of distribution: not established • Salivary concentrations:  it is not known whether methsuximide and N-desmethylmethsuximide are secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma Metabolism: • Methsuximide is rapidly metabolized in the liver to its primary metabolite N-desmethylmethsuximide, which is then further hydroxylated before renal elimination • The primary metabolite of methsuximide, N-desmethylmeth­ suximide, is pharmacologically active • Autoinduction is not a feature of methsuximide metabolism Elimination: • The elimination half-life of methsuximide is 1.0–2.6 hours • The elimination half-life of N-desmethylmethsuximide is 34–80 hours in adults and 16–45 hours in children • Renal excretion:  <1% of an administered dose is excreted unchanged in urine

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Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on methsuximide: –– Phenytoin and phenobarbital can increase the clearance of N-desmethylmethsuximide and decrease N-desmethylmeth­ suximide plasma levels

the epilepsy prescriber’s guide to antiepileptic drugs • Interactions between AEDs: effects by methsuximide: –– Methsuximide can increase plasma levels of phenytoin and phenobarbital –– Methsuximide can decrease plasma levels of carbamazepine and lamotrigine • Interactions between AEDs and non-AED drugs:  effects on methsuximide: –– To date, there have been no reports of other non-AED drugs affecting the clearance of methsuximide and affecting methsuximide plasma levels • Interactions between AEDs and non-AED drugs:  effects by methsuximide: –– To date, there have been no reports of methsuximide affecting the clearance of other non-AED drugs and affecting their plasma levels

Hormonal contraception: • Methsuximide does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects

Pharmacodynamic drug interactions: • To date, none have been reported

M

Adverse effects The adverse effects of methsuximide are very similar to those caused by ethosuximide How drug causes adverse effects: • Mechanism by which methsuximide causes adverse effects has not been determined Common adverse effects: • Abdominal discomfort • Vomiting • Diarrhea • Hiccups • Headaches • Sedation, drowsiness, fatigue Life-threatening or dangerous adverse effects: • Bone marrow reactions such as granulocytopenia, thrombocytopenia, or pancytopenia • Systemic lupus erythematosus • Stevens-Johnson syndrome

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Rare and not life-threatening adverse effects: • Behavioral disturbances: nervousness, irritability, depression, hallucinations, and even psychosis • Attacks of hepatic porphyria may be precipitated by meth­ suximide • Proteinuria • Microscopic hematuria Weight change: • Weight gain is uncommon

Methsuximide

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Gastrointestinal adverse effects can improve when methsuximide is taken at the end of a meal

Dosing and use Usual dosage range: • Adults: 600–1200 mg/day • Children:  10–30 mg/kg/day (mean dose <30 kg body weight:  20 mg/kg/day; >30 kg body weight: 15 mg/kg/day) Available formulations: • Capsules: 150 mg, 300 mg How to dose: –– For adults: start treatment with 300 mg/day; at intervals of 5–7 days increase by 300 mg/day as needed and tolerated; maintenance dose generally 600–1200 mg/day in two daily doses –– Children: start treatment with approximately 10 mg/kg/day, which is one-third of the initial target dose; there can be two or more subsequent increases by the same amount at intervals of 5–7 days; maintenance dose generally 10–30 mg/kg/day, in two daily doses Dosing tips: • Methsuximide should be given preferably after meals • Because of the long half-life of N-desmethylmethsuximide, methsuximide can be taken twice daily

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How to withdraw drug: • May need to adjust dosage of concurrent medications as methsuximide is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Rapid discontinuation may increase the risk of seizures

the epilepsy prescriber’s guide to antiepileptic drugs • Dose can be decreased linearly at weekly intervals over a period of 1–3 months • Because recurrence of absence seizures may be subtle clinically, or because significant sub-clinical spike-and-wave discharges may require re-introduction of therapy, it is good practice to repeat an EEG 1–3 months after methsuximide has been discontinued

Tests and therapeutic drug monitoring: • There are no clear guidelines regarding the need to monitor blood counts for the rare occurrence of bone marrow suppression, and clinical education and observation is likely to provide the best probability of early detection; blood count can be determined after 2 months, then every 6 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at plasma N-desmethylmethsuximide levels of 10–40 mg/L (50–200 μmol/L) –– The conversion factor from mg/mL to μmol/mL is 4.92 (i.e., 1 mg/L = 4.92 μmol/L) –– Once the patient is doing well clinically, there is no need to determine blood levels routinely –– The reference range of N-desmethylmethsuximide in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– There are no data indicating the usefulness of monitoring N-desmethylmethsuximide by use of saliva

Dosing and use

Overdose: • Usually not fatal and symptoms include: stupor, coma, respiratory depression, nausea, vomiting • N-desmethylmethsuximide plasma levels above 40 mg/L cause toxicity, and levels above 150 mg/L have been associated with coma • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis does not remove methsuximide or N-desmethyl­ methsuximide from blood and, therefore, is not a useful procedure in cases of overdose

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Other warnings/precautions: • Patients should be instructed to promptly inform their physician if they develop a sore throat, fever or other signs or symptoms suggestive of an infection • Mental and/or physical abilities may be impaired Do not use: • In patients with generalized tonic–clonic seizures unless they also take a medication that is known to be effective against tonic–clonic seizures

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Special populations Renal impairment: • Renal impairment has little or no impact on methsuximide pharma­cokinetics Hepatic impairment: • Liver failure may lower the clearance and decrease the dosage requirements of methsuximide Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

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Elderly: • Methsuximide is used only very rarely in the elderly • Elderly patients are more susceptible to adverse effects (especially somnolence) and, therefore, often do better at lower doses • Because of an age-related reduction in renal and hepatic function, lower methsuximide doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities; however, the risk of pharmacokinetic interactions with methsuximide is minimal Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Methsuximide is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than levetiracetam monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • It is not known whether during pregnancy methsuximide pharmacokinetics change

the epilepsy prescriber’s guide to antiepileptic drugs

The overall place of methsuximide in the treatment of epilepsy The primary indication of methsuximide is in the treatment of childhood absence epilepsy. However, methsuximide appears to be less effective than ethosuximide. In contrast to ethosuximide, methsuximide has been reported to be effective as adjunctive therapy against partial seizures. Methsuximide has also been reported to be at times effective against myoclonic seizures, including juvenile myoclonic epilepsy and against astatic seizures (drop attacks)

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Methsuximide, overall role

Breast feeding • Breast milk: methsuximide: it is not known whether it is secreted into breast milk; N-desmethylmethsuximide:  it is not known whether it is secreted into breast milk • Breastfed infants: it is not known what plasma methsuximide and N-desmethylmethsuximide concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

Primary seizure types: • Childhood absence seizures Secondary seizure types: • Partial seizures • Myoclonic seizures, including juvenile myoclonic epilepsy • Astatic seizures (drop attacks) Potential advantages: • Methsuximide has a mostly benign adverse effect profile and severe adverse reactions are extremely rare Potential disadvantages: • Narrow spectrum of seizure protection, limited mostly to absence seizures, with some efficacy against partial seizures • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Besag FM, Berry DJ, Pool F. Methsuximide lowers lamotrigine blood levels:  a pharmacokinetic antiepileptic drug interaction. Epilepsia 2000; 41: 624–627.

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Browne TR, Feldman RG, Buchanan RA, Allan NC, FawcettVickers L, Szako GK, Mattson GF, Norman SE, Greenblatt DJ. Methsuximide for complex partial seizures:  efficacy, toxicity, clinical pharmacology, and drug interactions. Neurology 1983; 33: 414–418. Hurst DL. The use of methsuximide for juvenile myoclonic epilepsy. Annals of Neurology 1995; 38: 517. Strong JM, Abe T, Gibbs EL, Atkinson AJ. Plasma levels of methsuximide and N-desmethylmethsuximide during methsuximide therapy. Neurology 1974; 24: 250–255. Tennison MB, Greenwood RS, Miles MV. Methsuximide for intractable childhood seizures. Pediatrics 1991; 87: 186–189. Wilder BJ, Buchanan RA. Methsuximide for refractory complex partial seizures. Neurology 1981; 31: 741–744.

the epilepsy prescriber’s guide to antiepileptic drugs

Midazolam Therapeutics Chemical name and structure: Midazolam, 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazol [1,5-a][1,4]benzodiazepine, is available as midazolam HCl and is a white to light yellow crystalline compound, with a molecular weight of 362.25 and an empirical formula of C18H13ClFN3 • HCl. CH3

M

N C

Cl

N

C

C

N

Brand names: • Dalam; Doricum; Dormicum; Dormonid • Fortanest; Fulsed • Hypnovel • Ipnovel • Midacum; Midanium; Midazo; Midazol; Midazolam Torrex; Midolam; Midozor; Miloz; Mizolam • Relacum • Sedacum; Sopodorm • Uzolam • Versed

therapeutics

F

Generics available: • No Licensed indications for epilepsy: • There are none Licensed indications for non-epilepsy conditions: • Sedation (UK-SPC; FDA-PI) • Pre-operative induction of anesthesia (UK-SPC; FDA-PI) • Drug-induced amnesia (UK-SPC; FDA-PI) Nonlicensed use for epilepsy: • Acute repetitive seizures • Refractory neonatal seizures • Refractory status epilepticus (convulsive and nonconvulsive)

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Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Midazolam is potentially effective against all types of seizures and is not contraindicated for any form of epilepsy

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Mechanism of action: • Benzodiazepines bind to the neuronal GABA A receptor, a ligandgated chloride channel • Benzodiazepines do not act directly on the chloride channel, but enhance binding of GABA to the receptor • When GABA binds to the GABA A receptor, it increases the frequency, but not the duration, of the opening of the chloride ion channel, which results in hyperpolarization of the membrane and reduction in neuronal firing • Activation of the chloride channel enhances inhibitory neuro­ transmission • Benzodiazepines also influence sodium channel function at high concentrations Efficacy profile: • The goal of treatment is complete remission of seizures • The onset of action is very rapid, particularly after intravenous administration • Like other benzodiazepines, midazolam often loses its efficacy during chronic use • Chronic use of midazolam in the treatment of epilepsy is unusual • Intravenous injection: onset 3–5 minutes • Intramuscular injection: onset 15 minutes, peak 20–30 minutes • Patients generally recover 2–6 hours after awakening

Pharmacokinetics Absorption and distribution: • Oral bioavailability: first pass hepatic transformation decreases the absolute systemic bioavailability of oral midazolam to 40–50% (27% in children) of that following intravenous administration • After rectal administration (solution) absolute bioavailability is ~50% • Food co-ingestion: neither the rate of absorption or the extent of absorption are affected by food co-ingestion • Tmax: ~1 hour (oral), 20–30 minutes (intramuscular); ~30 minutes (rectal) • Intranasal administration of midazolam is followed by very rapid absorption, and a time to seizure control of 2.5–5 minutes has been reported

the epilepsy prescriber’s guide to antiepileptic drugs • After intravenous administration, there is rapid distribution, with a distribution half-life of 6–15 minutes • Time to steady state: not appropriate • Pharmacokinetics: linear • Protein binding:  96–98% (midazolam); 89% (1-hydroxymida­ zolam) • Volume of distribution: 1.0–2.5 L/kg • Salivary concentrations:  it is not known whether midazolam or 1-hydroxymidazolam are secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

Drug interaction profile

Metabolism: • Midazolam is rapidly metabolized in the liver, primarily by CYP3A4, to 1-hydroxymidazolam (~63–80% of an administered dose) and to two minor metabolites (a 4-hydroxy metabolite [~3% of the dose] and a 1,4-dihydroxy metabolite [~1% of the dose]) • 1-hydroxymidazolam and its two minor metabolites are subsequently glucuronidated and eliminated predominantly through the kidneys • 1-hydroxymidazolam has weak pharmacological activity (approximately 10% of the pharmacological activity of midazolam after intravenous administration) • Autoinduction is not a feature of midazolam metabolism

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Elimination: • The elimination half-life of midazolam is 1.5–4 hours in adults • The elimination half-life of midazolam is 1–3 hours in children and can be as long as 6.5–12 hours in sick neonates • Renal excretion: <1% of the midazolam dose is excreted unchanged in the urine

Drug interaction profile Pharmacokinetic drug interactions • Interactions between AEDs: effects on midazolam: –– Carbamazepine, phenytoin, phenobarbital, and primidone can increase the clearance of midazolam and can decrease midazolam plasma levels • Interactions between AEDs: effects by midazolam: –– To date, there have been no reports of midazolam affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on midazolam: –– Cimetidine, clarithromycin, diltiazem, erythromycin, fluconazole, grapefruit juice, itraconazole, ketoconazole, ranitidine, roxithromycin, saquinavir, and verapamil can decrease the clearance of midazolam and increase midazolam plasma levels

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–– Rifampin can increase the clearance of midazolam and decrease midazolam plasma levels • Interactions between AEDs and non-AED drugs:  effects by midazolam: –– To date, there have been no reports of midazolam affecting the clearance of other non-AED drugs and affecting their plasma levels

Midazolam

Pharmacodynamic drug interactions: • Patients receiving long-term therapy with other benzodiazepines may be less responsive to midazolam in status epilepticus • The cardiovascular and respiratory depression by midazolam can be exacerbated by co-medication with phenobarbital • Midazolam may potentiate the action of CNS depressant drugs • Midazolam decreases the minimum alveolar concentration of halothane needed for general anesthesia • Hypotension has occurred in neonates given midazolam and fentanyl Hormonal contraception: • Midazolam does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects How drug causes adverse effects: • Mechanism by which midazolam causes adverse effects is probably the same as for seizure protection: enhancement of inhibitory neurotransmission through activation of the chloride ion channel • Actions at benzodiazepine receptors that carry over to the next day can cause daytime sedation, amnesia, and ataxia

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Common adverse effects: • Over-sedation: impaired recall, agitation, involuntary movements, headache • Drowsiness, fatigue • Ataxia • Psychomotor slowing • Cognitive dysfunction • Respiratory depression • Hypotension • Paradoxical reactions including agitation, restlessness, and hyper­ activity • Nausea, vomiting • Irritation/pain at site of injection

the epilepsy prescriber’s guide to antiepileptic drugs Life-threatening or dangerous adverse effects: • Other than respiratory depression, midazolam has no life-threatening or dangerous adverse effects • Hypersensitivity reactions are very rare • Respiratory depression, apnea, respiratory arrest • Cardiac arrest

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Rare and not life-threatening adverse effects: • Skin rash, urticarial reaction, pruritus at site of injection • Euphoria, hallucinations • Anterograde amnesia Weight change: • Not common; weight gain reported but not expected

Dosing and use

What to do about adverse effects: • Because midazolam is most commonly used in emergency situations, the only adverse effect that is of major relevance is respiratory depression • All patients given midazolam for repetitive seizures or status epilepticus should be monitored carefully for respiratory depression; adequate supportive equipment should be readily available

Dosing and use Usual dosage range: • The recommended initial intravenous bolus dose of midazolam is 0.15 mg/kg, administered over 2–5 minutes (no more than 2 mg/min) • If necessary, the initial intravenous bolus may be followed by continuous intravenous infusion at an initial rate of 1 µg/kg/min Available formulations: • Tablets: 15 mg • Syrup: 2 mg/mL (2.5 mL bottle or 118 mL bottle) • Ampoules for iv, im, and rectal administration:  10 mg/2 mL, 10 mg/5 mL • Ampoules for injection:  5 mg/mL, 10 mg/2 mL, 15 mg/3 mL, 25 mg/5 mL, 50 mg/10 mL, 90 mg/18 mL How to dose: • In most instances, midazolam is administered acutely or subacutely as described above • The intravenous loading dose of midazolam should be administered over 2–5 minutes or no more than 2 mg/min • The infusion rate may be increased by 1 µg/kg/min every 15 ­m inutes until seizure control is achieved

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• Seizure control is often achieved at infusion rates of < 3 µg/ kg/min • The use of rates up to 18 µg/kg/min has been reported • The recommended intramuscular dose is 5–10 mg in adults (0.2 mg/kg in children); this dose can be repeated once • The recommended intranasal and buccal dose is also 5–10 mg in adults (0.2 mg/kg in children) Dosing tips: • Better to under-dose, observe for effects, and then prudently raise dose while monitoring carefully • Although bioavailability after intramuscular administration is good (~80%), there is considerable inter-patient variability

Midazolam

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as midazolam is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Abrupt discontinuation of midazolam may be associated with withdrawal seizures • After acute or sub-acute treatment with repeated doses or intravenous infusion, the dose should be tapered down over 2–3 days • Chronic use of midazolam for the treatment of epilepsy is exceedingly rare Overdose: • Overdose with a benzodiazepine can cause all of the adverse effects listed above and can lead to severe respiratory depression, hypotension, coma, and death • Treatment of overdoses consists of supportive care and the administration of the benzodiazepine receptor antagonist flumazenil • The stomach should be emptied immediately by lavage or by induction of emesis • It is not known whether hemodialysis removes midazolam from blood and, therefore, could serve as a useful procedure in case of overdose

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Tests and therapeutic drug monitoring: • There is no need to monitor any laboratory parameter during treatment with midazolam • Therapeutic drug monitoring: uncommon –– Subjective CNS effects have been reported at threshold plasma levels of 30–100 μg/L (82.8–276 nmol/L), and mean peak plasma levels after 1 mg/kg orally in patients 2–12 years old was approximately 200 μg/L (552 nmol/L). A therapeutic range is not used clinically. –– The conversion factor from mg/mL to μmol/L, or μg/mL to nmol/L, is 2.76 (i.e., 1 μg/L = 2.76 nmol/L)

the epilepsy prescriber’s guide to antiepileptic drugs –– There are no data indicating the usefulness of monitoring midazolam by use of saliva

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Other warnings/precautions: • Patients should be monitored carefully for evidence of respiratory depression, accumulation of secretions and impairment of swallowing • Patients with chronic obstructive pulmonary disease should receive lower doses • Use with caution in patients with impaired respiratory function

Special populations Renal impairment: • Renal failure may prolong the half-life of midazolam

Special populations

Do not use: • Use with caution in patients with a history of paradoxical reaction to midazolam, or to other benzodiazepines • If patient has narrow angle-closure glaucoma

Hepatic impairment: • Severe hepatic failure may prolong the half-life of midazolam Children: • Children do not require additional precautions or monitoring • In sick neonates, clearance is reduced and the elimination half-life of midazolam is longer (6.5–12 hours) • Seriously ill neonates have reduced clearance and longer elimination half-life values Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, often do better at lower doses • The elimination half-life of midazolam may be prolonged in the elderly Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Midazolam is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; ­potential

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benefits may still justify its use during pregnancy, especially of seizure disorders] • Possible increased risk of birth defects when benzodiazepines are taken during pregnancy • Infants whose mothers received a benzodiazepine late in pregnancy may experience withdrawal effects • Neonatal flaccidity has been reported in infants whose mothers took a benzodiazepine during pregnancy • Midazolam is virtually never used as an antiepileptic drug for a sufficiently long time to have an impact on the pregnancy or the fetus

Midazolam

Breast feeding • Breast milk: transfer into breast milk is minimal because of extensive binding to plasma proteins • Midazolam is virtually never used as an antiepileptic drug for a sufficiently long time to have an impact on breast feeding • Breastfed infants: it is not known what plasma midazolam concentrations are achieved in breastfed infants compared with the levels of their mothers • Effects on infant have been observed and include feeding difficulties, sedation, and weight loss • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

The overall place of midazolam in the treatment of epilepsy As is the case with some other benzodiazepines, midazolam use in the treatment of epilepsy is largely limited to acute and sub-acute management of convulsive and nonconvulsive seizures. Midazolam is the only drug used in the management of status epilepticus which can be given by rectal administration or by intramuscular or intravenous injection. Its intramuscular use in premonitory status is a great advantage, and midazolam has an important clinical role at this stage in status as an alternative to intravenous or rectal diazepam. Primary seizure types: • Status epilepticus Secondary seizure types: • None

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Potential advantages: • Midazolam is very rapidly absorbed following intramuscular and intranasal administration

the epilepsy prescriber’s guide to antiepileptic drugs • Midazolam has a relatively short half-life and is well suited for continuous intravenous infusion • Midazolam has virtually no organ toxicity • Has less tendency to accumulate than diazepam

Suggested reading Bell DM, Richards G, Dhillon S, Oxley JR, Cromarty J, Sander JW, Patsalos PN. A comparative pharmacokinetic study of intravenous and intramuscular midazolam in patients with epilepsy. Epilepsy Research 1991; 10: 183–190. Chamberlain JM, Altieri MA, Futterman C, Young GM, Ochsenschlager DW, Waisman Y. A prospective, randomized study comparing intramuscular midazolam with intravenous diazepam for the treatment of seizures in children. Pediatric Emergency Care 1997; 13: 92–94. Claassen J, Hirsch LJ, Emerson RG, Bates JE, Thompson TB, Mayer SA. Continuous EEG monitoring and midazolam infusion for refractory nonconvulsive status epilepticus. Neurology 2001; 57: 1036–1042. Holmes GL, Riviello JJ Jr. Midazolam and pentobarbital for refractory status epilepticus. Pediatric Neurology 1999; 20: 259–264. Koul RL, Aithala GR, Chacko A, Joshi R, Elbualy MS. Continuous midazolam as treatment of status epilepticus. Archives of Diseases of Childhood 1997; 76: 445–448. Lahat E, Goldman M, Barr J, Eshel G, Berkovitch M. Intranasal midazolam for childhood seizures. Lancet 1998; 352: 620. Prasad K, Al-Roomi K, Krishnan PR, Sequeira R. Anticonvulsant therapy for status epilepticus. Cochrane Database of Systematic Reviews 2005;4:CD003723. Riviello JJ Jr, Holmes GL. The treatment of status epilepticus. Seminars in Pediatric Neurolology 2004; 11: 129–138.

Midazolam, overall role

Potential disadvantages: • The effectiveness of midazolam in the chronic treatment of epilepsy is limited by its sedative and behavioral effects, by its short elimination half-life and by the development of tolerance to the protective effect against seizures • Abrupt discontinuation of midazolam, and benzodiazepines in general, can lead to withdrawal seizures and withdrawal symptoms • Short acting with tendency to relapse following a single injection • The lipid solubility of midazolam and hence its cerebral action are reduced as blood and cerebral pH fall • Elimination dependent on blood flow • Potential teratogen, but not more than most other antiepileptic drugs

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Midazolam 162

Sheth RD, Buckley DJ, Gutierrez AR, Gingold M, Bodensteiner JB, Penney S. Midazolam in the treatment of refractory neonatal seizures. Clinical Neuropharmacology 1996; 19: 165–170. Singhi S, Murthy A, Singhi P, Jayashree M. Continuous midazolam versus diazepam infusion for refractory convulsive status epilepticus. Jounal of Child Neurology 2002; 17: 106–110.

the epilepsy prescriber’s guide to antiepileptic drugs

Oxcarbazepine Therapeutics Chemical name and structure: Oxcarbazepine, 10,11-dihydro-10-oxo-5H-dibenz (b,f ) azepine4-carboxamide, is a white to faintly orange crystalline powder, with a molecular weight of 252.27 and an empirical formula of C15H12N2O2 .

O

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N NH2 Brand names: • Actinium; Apydan extent • Deprectal • Lonazet • Neurtrol • Oxetol; Oxrate • Prolepsi • Timox; Trexapin; Trileptal; Trileptin

therapeutics

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Generics available: • Yes Licensed indications for epilepsy: • Monotherapy or adjunctive treatment of partial seizures with or without secondary generalization in patients ≥ 6 years of age (UK-SPC; EMEA-SPC) • Monotherapy for the treatment of partial seizures with or without secondary generalization in patients ≥ 4 years of age (FDA-PI) • Adjunctive treatment of partial seizures with or without secondary generalization in patients ≥ 2 years of age (FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • There are none

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Nonlicensed use for non-epilepsy conditions: • Bipolar disorder • Trigeminal neuralgia Ineffective (contraindicated): • Oxcarbazepine is contraindicated for generalized seizures such as absences or myoclonic jerks in syndromes of idiopathic generalized epilepsies; this may be the result of oxcarbazepine per se and not of its pharmacologically active metabolite 10-hydroxycarbazepine • It may be ineffective in neonates and children < 2 years of age

Oxcarbazepine

Mechanism of action: • The pharmacological activity of oxcarbazepine is primarily exerted through its 10-monohydroxy metabolite (hydroxy-10,11-dihydro5H-dibenzapine-5-carboxamide) • Acts as a use-dependent blocker of voltage-sensitive sodium channels • This results in stabilization of hyper-excited neural membranes, inhibition of repetitive neuronal firing and diminution of propagation of synaptic impulses so that seizure spread is prevented • Increases potassium conductance • Modulates high-voltage activated calcium channels and reduces the release of glutamate Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 2 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If oxcarbazepine is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: 100% (oxcarbazepine) • Food co-ingestion:  neither delays the rate of absorption nor decreases the extent of absorption (oxcarbazepine) • Tmax: 3–6 hours (oxcarbazepine) • Time to steady state: 2–3 days (10-hydroxycarbazepine) • Pharmacokinetics: linear • Protein binding:  40% (10-hydroxycarbazepine); 60% (oxcarba­ zepine) • Volume of distribution: 0.75 L/kg (10-hydroxycarbazepine) • Salivary concentrations: 10-hydroxycarbazepine is secreted into saliva and concentrations are similar to the unbound levels seen in plasma

the epilepsy prescriber’s guide to antiepileptic drugs

Elimination: • Half-life of oxcarbazepine is ~2 hours; thus oxcarbazepine is essentially a prodrug rapidly converted to its 10-hydroxycarbazepine metabolite • In the absence of enzyme inducing co-medication, half-life values for 10-hydroxycarbazepine are 8–15 hours • In the presence of enzyme inducing co-medication, half-life values for 10-hydroxycarbazepine are 7–12 hours • Renal excretion:  >95% of an administered dose is excreted as metabolites in urine; 49% as glucuronides of 10-hydroxycarbazepine and 27% as unchanged 10-hydroxycarbazepine • Renal excretion: <1% of an administered dose is excreted unchanged as oxcarbazepine in urine Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on 10-hydroxycarbazepine: –– Carbamazepine, phenobarbital, phenytoin, and primidone can increase the clearance of 10-hydroxycarbazepine and decrease 10-hydroxycarbazepine plasma levels –– Valproic acid can displace 10-hydroxycarbazepine from its plasma protein binding sites • Interactions between AEDs: effects by 10-hydroxycarbazepine: –– 10-hydroxycarbazepine can decrease plasma levels of carbamazepine, lamotrigine, and topiramate –– 10-hydroxycarbazepine can increase plasma levels of phenobarbital and phenytoin • Interactions between AEDs and non-AED drugs:  effects on 10-hydroxycarbazepine: –– Viloxazine can increase 10-hydroxycarbazepine plasma levels –– Verapamil can decrease 10-hydroxycarbazepine plasma levels –– Oral contraceptives can increase the clearance of 10-hydroxycarbazepine and decrease 10-hydroxycarbazepine plasma levels

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Drug interaction profile

Metabolism: • Oxcarbazepine is rapidly metabolized in the liver to its pharmacologically active metabolite, 10-hydroxycarbazepine (also known as licarbazepine), by stereoselective biotransformation mediated by cytosolic arylketone reductase • 10-hydroxycarbazepine comprises of a racemic mixture of 80% S (active) and 20% R (inactive) • 10-hydroxycarbazepine is subsequently primarily metabolized by conjugation with glucuronic acid • Minor amounts (4% of dose) of 10-hydroxycarbazepine are oxidized to an inactive 10,11-dihydroxy metabolite • Metabolites (other than 10-hydroxycarbazepine) are not pharmacologically active • Autoinduction is not a feature of oxcarbazepine metabolism

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• Interactions between AEDs and non-AED drugs:  effects by 10-hydroxycarbazepine: –– 10-hydroxycarbazepine can decrease plasma levels of felodipine Pharmacodynamic drug interactions: • Concomitant administration with lamotrigine has been associated with an increased risk of adverse effects (nausea, somnolence, dizziness, and headache) • Concomitant administration with lithium has been associated with enhanced neurotoxicity

Oxcarbazepine

Hormonal contraception: • Oxcarbazepine enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking oxcarbazepine

Adverse effects How drug causes adverse effects: • CNS adverse effects may be due to excessive actions at voltagesensitive sodium channels Common adverse effects: • Somnolence, dizziness, headache • Depression, apathy, agitation, confusional state • Diplopia, blurred vision, vertigo • Nausea, vomiting • Hyponatremia • Rash, alopecia, acne • Fatigue, asthenia

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Life-threatening or dangerous adverse effects: • Rare dermatological reactions, including Stevens-Johnson syndrome, toxic epidermal necrolysis (Lyell syndrome) and erythema multiforme; median time of onset is 19 days • Skin rash rate is 5% with oxcarbazepine versus 10–15% with carbamazepine and typically 25% of patients presenting with skin rash with carbamazepine will also have skin rash with oxcarbazepine • Hypersensitivity reactions, including multi-organ hypersensitivity reactions, may occur: oxcarbazepine should be withdrawn immediately if these symptoms present • Hyponatremia (sodium levels <125 mmol/L) • Very rarely agranulocytosis, aplastic anemia, pancytopenia, and thrombocytopenia • Arrhythmia, atrioventricular block

the epilepsy prescriber’s guide to antiepileptic drugs Rare and not life-threatening adverse effects: • Hepatitis • Pancreatitis

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Weight change • Not common; weight gain reported but not expected What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Sedation is dose-related and can subside with time • Lower the dose

Dosing and use

Dosing and use Usual dosage range: • Adults: 600–2400 mg/day • Children: –– 600–900 mg/day – for body weight of <20 kg –– 900–1200 mg/day – for body weight of 20–29 kg –– 900–1500 mg/day – for body weight of 30–39 kg –– 1500–1800 mg/day – for body weight 40–59 kg Available formulations: • Tablets: 150 mg, 300 mg, 600 mg • Oral suspension: 300 mg/5 mL How to dose: • When initiating oxcarbazepine treatment start with a low dose and titrate slowly so as to minimize adverse effects. –– For adults: start treatment with 300 mg/day in 2 divided doses; subsequently in 2-day intervals increase in steps of 150 mg daily; maintenance dose generally up to 2400 mg/day given in 2 equally divided doses –– Children 2–16 years old: start treatment with 10 mg/kg/day in 2 divided doses; subsequently increase in steps of 10 mg/kg/day at weekly intervals to a maximum of 30–45 mg/kg/day; maintenance dose generally up to 1800 mg/day (depending on body weight) given in 2 equally divided doses Dosing tips: • Titration of dose should be undertaken based on individual tolerability and response to the drug

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Oxcarbazepine 168

• Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating adverse effects • Should titrate slowly in the presence of other sedating agents, such as other antiepileptic drugs to best tolerate additive sedative adverse effects • Doses of oxcarbazepine need to be approximately one-third higher than those of carbamazepine for similar results • Suspension formulation, which is useful for patients with difficulties swallowing, can be administered mixed in a glass of water or directly from the oral dosing syringe supplied • Patients who have exhibited a skin rash with carbamazepine should be informed that ~25–30% of them will experience a skin rash with oxcarbazepine How to withdraw drug: • May need to adjust dosage of concurrent medications as oxcarbazepine is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper:  a gradual dose reduction over a minimum of a 1-week period should be undertaken • Rapid discontinuation may induce withdrawal seizures Overdose: • In overdoses up to 24 g, no unexpected adverse effects were observed • The most common adverse effects observed with oxcarbazepine overdose include somnolence, dizziness, nausea, vomiting, hyperkinesia, hyponatremia, ataxia, and nystagmus • If indicated the stomach should be emptied by lavage or by induction of emesis • It is not known whether hemodialysis removes oxcarbazepine and 10-hydroxycarbazepine from blood and, therefore, could serve as a useful procedure in case of overdose Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests including sodium levels • During treatment: liver and kidney function tests including sodium levels every 12 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at plasma 10-hydroxycarbazepine concentrations of 3–35 mg/L (12–137 μmol/L) –– The conversion factor from mg/L to μmol/L is 3.96 (i.e., 1 mg/L = 3.96 μmol/L) –– The reference range of 10-hydroxycarbazepine in plasma is considered to be the same for children and adults although no data are available to support this clinical practice

the epilepsy prescriber’s guide to antiepileptic drugs –– 10-hydroxycarbazepine can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant

special populations

Other warnings/precautions: • Use cautiously in patients who have demonstrated hypersensitivity to carbamazepine • Because oxcarbazepine has a tricyclic chemical structure, it is not recommended to be taken with MAOIs, including 14 days after MAOIs are stopped; do not start an MAOI until 2 weeks after discontinuing oxcarbazepine • May exacerbate narrow angle-closure glaucoma • In patients with pre-existing renal conditions associated with low sodium or in patients treated with sodium-lowering medications (e.g., diuretics, desmopressin, nonsteroidal anti-inflammatory drugs [e.g., indometacin]) blood sodium levels should be measured before initiating treatment with oxcarbazepine; thereafter, sodium levels should be measured after ~2 weeks and then at monthly intervals for the first 3 months or according to clinical need • Usually hyponatremia (sodium levels <125 mmol/L) is asymptomatic and dose adjustment is not necessary; however, if it becomes clinically significant (typically occurs in 2–3% of patients), it generally occurs within 3 months of treatment initiation and usually can be reversed by either restricting fluid intake or a reduction in oxcarbazepine dose • Patients with cardiac insufficiency and secondary heart failure should be weighed regularly as an index of fluid retention; if worsening of the cardiac condition occurs or fluid retention with concurrent hyponatremia is observed, the use of water restriction is the countermeasure of choice • Rarely oxcarbazepine may lead to impairment of cardiac conductance and patients with pre-existing conduction disturbances (e.g., atrioventricular-block, arrhythmia) should be followed carefully • Some patients may experience dizziness and somnolence and thus caution needs to be exercised if patient intends to drive or use machinery

O

Do not use: • If patient has a proven allergy to oxcarbazepine or to any of the excipients • If patient is taking an MAOI • If a patient has hypersensitivity to other carboxamide derivatives (e.g. carbamazepine and eslicarbazepine acetate) Special populations Renal impairment: • Oxcarbazepine is renally excreted, so the dose needs to be adjusted according to creatinine clearance as follows:

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–– CrCl of <30 mL/min – starting dose: 300 mg/day taken twice a day; increase dose, in at least weekly intervals, to achieve desired clinical response Hepatic impairment: • Oxcarbazepine is extensively metabolized in the liver to 10-hydroxycarbazepine which is in turn substantially metabolized; consequently lower doses may be required in patients with hepatic impairment

Oxcarbazepine 170

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal function, lower oxcarbazepine doses are appropriate and should be based on creatinine clearance values • Because oxcarbazepine is associated with dizziness and somnolence the elderly are at increased risk of accidental injury (fall) • The elderly, with pre-existing renal conditions and who may be taking sodium lowering medications or nonsteroidal anti­inflammatory drugs, have an increased risk of developing symptomatic hyponatremia • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with oxcarbazepine is moderate Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a women is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures which could have serious consequences for the woman and the unborn child • Oxcarbazepine is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Oxcarbazepine is structurally similar to carbamazepine, which is thought to be teratogenic in humans

the epilepsy prescriber’s guide to antiepileptic drugs

Breast feeding • Breast milk: 10-hydroxycarbazepine: 50–80% of maternal plasma levels • Breastfed infants: 10-hydroxycarbazepine plasma levels are 7–12% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

O

Oxcarbazepine, overall role

• Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than oxcarbazepine monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • During pregnancy oxcarbazepine pharmacokinetics change significantly so that 10-hydroxycarbazepine concentrations decrease by 30–36% due to increased clearance consequent to enhanced glucuronidation; an increase in oxcarbazepine dose may be required in some patients

The overall place of oxcarbazepine in the treatment of epilepsy Oxcarbazepine is similar to carbamazepine in its antiepileptic efficacy in that it is effective both as monotherapy and as adjunctive therapy for all types of partial seizures with or without secondarily generalization. May be particularly useful in patients unable to tolerate carbamazepine but who respond to carbamazepine. Primary seizure types: • Partial seizures Secondary seizure types • None Potential advantages: • Oxcarbazepine is better tolerated than carbamazepine probably because it is not metabolized to the pharmacologically active metabolite carbamazepine-epoxide • Oxcarbazepine has much less prominent actions on CYP 450 enzyme systems than carbamazepine, and thus fewer pharmacokinetic interactions • Skin rash reactions to carbamazepine may resolve in 75% of patients when switched to oxcarbazepine; thus, 25% of patients who experience rash with carbamazepine may also experience it with oxcarbazepine

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Oxcarbazepine 172

Potential disadvantages: • Patients are at greater risk of hyponatremia than with carbama­ zepine • May need to restrict fluid and/or monitor sodium because of risk of hyponatremia • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Bang LM, Goa KL. Spotlight on oxcarbazepine in epilepsy. CNS Drugs 2004; 18: 57–61. Christensen J, Sabers A, Sidenius P. Oxcarbazepine concentrations during pregnancy: a retrospective study in patients with epilepsy. Neurology 2006; 67: 1497–1499. Gelisse P, Genton P, Kuate D, Pesenti A, Baldy-Moulinier M, Crespel A. Worsening of seizures by oxcarbazepine in juvenile idiopathic generalized epilepsies. Epilepsia 2004; 45: 1282–1288. Johannessen Landmark S, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Rouan MC, Lecaillon JB, Godbillon J, Menard F, Darragon T, Meyer P, Kourilsky O, Hillion D, Aldigier JC, Jungers P. The effect of renal impairment on the pharmacokinetics of oxcarbazepine and its metabolites. European Journal of Clinical Pharmacology 1994; 47:161–167. Schmidt D, Elger CE. What is the evidence that oxcarbazepine and carbamazepine are distinctly different antiepileptic drugs? Epilepsy & Behavior 2004; 5: 627–635. Zheng T, Clarke AL, Morris MJ, Reid CA, Petrou S, O’Brien TJ. Oxcarbazepine, not its active metabolite, potentiates GABA A activation and aggravates absence seizures. Epilepsia 2009; 50: 83–87.

the epilepsy prescriber’s guide to antiepileptic drugs

Paraldehyde Therapeutics Chemical name and structure: Paraldehyde, a cyclic polymer of acetaldehyde (2,4,6-trimethyl1,3,5-trioxane), is a colorless liquid, with a molecular weight of 132.2 and an empirical formula of C6H12O3. It crystallizes at and below 12°C. CH3

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CH3

O O

O

CH3

Generics available: • Yes Licensed indications for epilepsy: • Management of status epilepticus in children and adults (UK-SPC)

therapeutics

Brand names: • Paral

Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • Acute repetitive convulsive seizures refractory to traditional anti­ epileptic drug therapy Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Paraldehyde is practically never used chronically in the treatment of epileptic seizures Mechanism of action: • The mechanism by which paraldehyde exerts its anticonvulsant activity has not been established Efficacy profile: • It is for the treatment of status epilepticus, particularly when other drugs are inappropriate or ineffective • The onset of action is very rapid, particularly after intravenous administration

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: 90–100% • Rectal bioavailability: 75–90% • Food co-ingestion: it is not known whether the rate of absorption or the extent of absorption are affected by food co-ingestion • Tmax: ~0.5 hours (oral ingestion); ~1.5–2 hours (rectal administration); ~20–60 minutes (intramuscular administration) • Time to steady state:  not applicable (paraldehyde is practically never used chronically in the treatment of epileptic seizures) • Pharmacokinetics: linear • Protein binding: not known • Volume of distribution: 0.89 L/kg (adults); 3.18 L/kg (infants) • Salivary concentrations:  it is not known whether paraldehyde is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

Paraldehyde

Metabolism: • Approximately 70–90% of the dose is metabolized in the liver to acetaldehyde, which is then oxidized to acetic acid by the enzyme aldehyde dehydrogenase • Acetic acid is then metabolized further into carbon dioxide and water • Some of the drug (11–28%) is excreted unchanged through the lungs, which gives a characteristic unpleasant odor to the breath Elimination: • The elimination half-life of paraldehyde in neonates is 10.2–23.6 hours • The elimination half-life of paraldehyde in children and adults is 3.5–9.5 hours • Renal excretion:  <1% of an administered dose is excreted unchanged as paraldehyde in urine

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Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on paraldehyde: –– To date, there have been no reports of AEDs affecting the clearance of paraldehyde and affecting plasma levels • Interactions between AEDs: effects by paraldehyde: –– To date, there have been no reports of paraldehyde affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on paraldehyde: –– Disulfiram, which inhibits acetaldehyde dehydrogenase, can decrease the clearance of paraldehyde and increase paraldehyde (and acetaldehyde) plasma levels

the epilepsy prescriber’s guide to antiepileptic drugs • Interactions between AEDs and non-AED drugs:  effects by paraldehyde: –– To date, there have been no reports of paraldehyde affecting the clearance of other non-AED drugs and affecting their plasma levels

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Pharmacodynamic drug interactions: • Paraldehyde may potentiate the effect of other CNS depressants such as barbiturates and alcohol Hormonal contraception: • Because paraldehyde is only used for the acute treatment of seizures, its potential effect on hormonal contraception is of limited relevance

Common adverse effects: • Drowsiness, lethargy • Nausea, vomiting or abdominal pain, when administered orally • Muscle cramps • Unusual sweating • Unpleasant odor of breath • Allergic skin rash • Paraldehyde can be irritating to the eyes and to the skin • Yellow discoloration of the skin and eyes with long-term use

Adverse effects

Adverse effects How drug causes adverse effects: • Mechanism by which paraldehyde causes adverse effects has not been established

Life-threatening or dangerous adverse effects: • Metabolic acidosis, especially after administration of partly decomposed paraldehyde • Intravenous administration may cause pulmonary edema and hemorrhage, cardiac dilatation, and cardiovascular shock, and this route of administration should be discouraged • Hepatitis and nephrosis have been observed after prolonged use of paraldehyde • Deaths have been reported due to corrosive poisoning by decomposed paraldehyde • When a higher than 5% concentration is used for intravenous infusion, droplets of pure paraldehyde may form and act as emboli Rare and not life-threatening adverse effects: • Impaired coordination and ataxia • May aggravate colitis when given rectally

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• May aggravate gastric ulcer when given orally • May cause severe pain, redness, swelling or sterile abscess at intramuscular injection site, as well as thrombophlebitis when administered intravenously • Intramuscular injection close to nerve trunks may cause severe and permanent nerve damage • Intramuscular injection may cause severe causalgia if the injection is too close to the sciatic nerve Weight change: • Not common; paraldehyde is practically never used chronically in the treatment of epileptic seizures What to do about adverse effects: • Heart rate, respiration, and blood pressure must be monitored closely during paraldehyde administration

Paraldehyde

Dosing and use Usual dosage range: • Rectal: 1:1 paraldehyde:vegetable oil solution, 0.3 mL/kg per dose (300 mg/kg of paraldehyde); may repeat every 2–4 hours • Intramuscular:  adults 5–10 mL/dose, children 0.1–0.15 mL/kg/ dose, every 4–8 hours • Intravenous: 100–150 mg/kg (0.1–0.15 mL/kg) over 10–15 minutes, followed by a drip of 20 mg/kg/hour (0.4 mL/kg/hour of a 5% solution) • Maintenance: paraldehyde is virtually never administered chronically for the treatment of epileptic seizures Available formulations: • Ampoules (darkened glass): 5 mL/ampoule for intramuscular, rectal or intravenous administration (contains hydroquinone 100 μg/ mL as an antioxidant) How to dose: • For intravenous administration, paraldehyde should be diluted into a 5% solution by adding normal saline (20 mL of normal saline for each 1 mL of paraldehyde) • Dosages are commonly cited in volume units (e.g., mL) as well as mass units (e.g., grams) which for practical purposes can be considered equivalent (strictly speaking 1 mL weighs 1.006 g); 1 mL of paraldehyde is 1 g or 1000 mg of paraldehyde

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Dosing tips: • Never use any plastic containers, spoons, or syringes to administer paraldehyde, because of its solvent effect on plastic; use only glass or metal, unless the 5% solution is used

the epilepsy prescriber’s guide to antiepileptic drugs

How to withdraw drug: • Because paraldehyde is used only for the acute treatment of seizures, gradual withdrawal is not necessary Overdose: • Can be fatal: symptoms include confusion, nausea, vomiting, severe abdominal pain, weakness, oliguria, cloudy urine, metabolic acidosis, hyperventilation, respiratory depression, pulmonary edema, bradycardia, hypotension, cardiac failure, renal failure, toxic hepatitis, coma • Fatalities are uncommon and usually secondary to respiratory failure, heart failure or metabolic acidosis • The main aspect of treatment is respiratory support • Bicarbonate for metabolic acidosis and vasopressors for hypotension may be considered • The stomach should be emptied immediately by lavage or by induction of emesis • It is not known whether hemodialysis removes paraldehyde from blood and, therefore, could serve as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Electrolytes and blood gases may be obtained when metabolic acidosis is suspected • Therapeutic drug monitoring: because paraldehyde is not administered chronically, plasma level monitoring is not necessary or helpful • The minimum therapeutic plasma concentration for the control of status epilepticus is considered to be ~300 ng/mL

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Dosing and use

• Paraldehyde should be diluted with normal saline before intravenous administration • Before rectal administration, the paraldehyde solution should be mixed 1:1 with an equal volume of olive oil, peanut oil or other vegetable oil to reduce mucosal irritation • When taken orally, paraldehyde can be mixed with milk or fruit juice to reduce the unpleasant taste • Breakdown of paraldehyde, consequent to exposure to light, leads to a brownish discoloration and an acetic acid odor of the solution, indicating that it should no longer be used • Paraldehyde has a short shelf life and decomposes after the container has been opened • Administration of partly decomposed paraldehyde is highly toxic and may cause:  metabolic acidosis or death if administered by injection; severe proctitis and excoriating anal rash or even large bowel perforation if administered by means of the rectal route

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Other warnings/precautions: • Patients should be monitored carefully for signs of unusual bleeding or bruising • Heart rate, respiration, and blood pressure must be monitored closely during administration Do not use: • Rectally in patients with colitis • Orally in patients with gastric ulcer • In patients with chronic lung disease, such as emphysema, asthma, or bronchitis • In patients with severe hepatic failure • In patients with a history of hypersensitivity to paraldehyde

Paraldehyde

Special populations Renal impairment: • Renal impairment has little or no impact on paraldehyde pharmacokinetics and elimination Hepatic impairment: • Hepatic impairment may lead to decreased clearance of paraldehyde • Paraldehyde is contraindicated in patients with severe hepatic failure Children: • No specific or different information is available on children Elderly: • No information available Pregnancy: • Paraldehyde is virtually never administered chronically for the treatment of epileptic seizures • Paraldehyde is classified by the US Food and Drug Administration as risk category D (positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy) • Paraldehyde should not be used during labor, because it diffuses across the placenta and has been shown to cause respiratory depression in newborns

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Breast feeding • Breast milk:  it is not known whether it is secreted into breast milk • Breastfed infants: it is not known what plasma paraldehyde concentrations are achieved in breastfed infants compared with the levels of their mothers

the epilepsy prescriber’s guide to antiepileptic drugs

Primary seizure types: • The use of paraldehyde in the treatment of epilepsy is practically limited to the treatment of acute convulsive seizures or convulsive status epilepticus Secondary seizure types: • None Potential advantages: • Paraldehyde can be administered rectally or intramuscularly when no venous access is available • Seizures do not often recur after seizure control has been established • Longer duration of action compared with other benzodiazepines

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Paraldehyde, overall role

The overall place of paraldehyde in the treatment of epilepsy Although paraldehyde is an old-fashioned medication (first introduced into clinical practice in 1882), it still has a place in the treatment of status epilepticus and is indeed widely used in institutions/ hospitals that are experienced in the treatment of epilepsy. It is now used primarily as an alternative to diazepam or subsequent to diazepam administration for premonitory or early and established status epilepticus. Paraldehyde is particularly useful where intravenous administration is difficult or where conventional antiepileptic drugs are contraindicated or have proved ineffective. The drug is usually given rectally or intramuscularly and absorption is fast and complete.

Potential disadvantages: • Paraldehyde has a slower onset of action and lesser efficacy compared with the current traditional therapies of status epilepticus • Decomposed or inadequately diluted solutions are highly toxic • Intravenous administration carries the risk of potentially serious toxic effects and careful monitoring is essential

Suggested reading Ahmad S, Ellis JC, Amend H, Molyneux E. Efficacy and safety of intranasal lorazepam versus intramuscular paraldehyde for protracted convulsions in children: an open randomized trial. Lancet 2006; 367: 1555–1556. Appleton R, Macleod S, Maryland T. Drug management for acute tonic-clonic convulsions including convulsive status epilepticus in children. Cochrane Database of Systematic Reviews 2008; 3: CD001905. Armstrong DL, Battin MR. Pervasive seizures caused by hypoxicischemic encephalopathy:  treatment with intravenous paraldehyde. Journal of Child Neurology 2001; 16: 915–917.

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Paraldehyde 180

Bostrom B. Paraldehyde toxicity during treatment of status epilep­ ticus. American Journal of Diseases in Children 1982; 136: 414–415. Chin RF, Neville BG, Packham C, Wade A, Bedford H, Scott RC. Treatment of community-onset, childhood convulsive status epilepticus: a prospective, population-based study. Lancet Neurology 2008; 7: 696–703. Curless RG, Holzman BH, Ramsay RE. Paraldehyde therapy in childhood status epilepticus. Archives of Neurology 1983; 40: 477–480. Johnson CE, Vigoreaux JA. Compatibility of paraldehyde with plastic syringes and needle hubs. American Journal of Hospital Pharmacy 1984; 41: 306–308. Ramsay RE. Pharmacokinetics and parenteral use of phenytoin, phenobarbital, and paraldehyde. Epilepsia 1989; 30(Suppl 2): S1–S3. Welty TE, Cloyd JC, Abdel-Monem MM. Delivery of paraldehyde in 5% dextrose and 0.9% sodium chloride injections through poly­v inyl chloride IV sets and burettes. American Journal of Hospital Pharmacy 1988; 45: 131–135.

the epilepsy prescriber’s guide to antiepileptic drugs

Phenobarbital Therapeutics Chemical name and structure: Phenobarbital, 5-ethyl-5-phenylbarbituric acid, is a white powder, with a molecular weight of 232.23 and an empirical formula of C12H12N2O3. O

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H N O N

O

H

therapeutics

Brand names: • Alepsal; Ancalixir; Andral; Aphenylbarbit; Atrofen • Barbilettae; Barbilixir; Barbiphenyl; Bialminal • Comizial • Dormital • Edhanol • Fenemal; Fenobarbital; Fenobarbitale; Fenobarbitale Sodico; Fenton • Gardenal; Gardenal Sodium; Gardenale; Gratusminal • Lepinal natrium; Lethyl; Lumcalcio; Luminal; Luminale; Luminaletas; Luminalette; Luminaletten; Luminalum • Menobarb • Neurobiol • Pevalon; Phenaemal; Phenobarbiton; Phenobarbiton-natrium; Phenobarbitone; Phenotal • Sevenal; Solfoton • Tridezibarbitur • Uni-Feno Generics available: • Yes Licensed indications for epilepsy: • Generalized tonic–clonic and partial seizures in patients of any age (FDA-PI) • All forms of epilepsy, except absence seizures, in patients of any age (UK-BNF) Licensed indications for non-epilepsy conditions: • Sedative/hypnotic (FDA-PI)

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Nonlicensed use for epilepsy: • Acute convulsive episodes and status epilepticus • Lennox-Gastaut syndrome • Myoclonic seizures • Neonatal seizures • Prophylaxis of febrile seizures Nonlicensed use for non-epilepsy conditions: • Treatment of sedative or hypnotic drug withdrawal Ineffective (contraindicated): • Absence seizures

Phenobarbital 182

Mechanism of action: • Enhancement of γ-aminobutyric acid (GABA) inhibition • Enhances postsynaptic GABA A receptor-mediated chloride currents by prolonging the opening of the chloride ionophore • Concentration-dependent reduction of calcium-dependent action potentials Efficacy profile: • The goal of treatment is complete remission of seizures • Onset of action is rapid following intravenous administration • In the absence of a loading dose, maintenance doses do not achieve a steady-state level until approximately 2–3 weeks, because of the long elimination half-life; accordingly, the onset of action may be delayed • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • Phenobarbital is a drug of first choice only in neonates with seizures • Phenobarbital is a drug of third choice for the intravenous treatment of status epilepticus, after a benzodiazepine and phenytoin • If phenobarbital is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Pharmacokinetics Absorption and distribution: • Oral bioavailability: >90% (tablets) • Bioavailability:  >90% after intramuscular administration (parenteral solution); 90% after rectal administration (parenteral solution) • Food co-ingestion: causes a slight delay in the rate of absorption but the extent of absorption is unaffected

the epilepsy prescriber’s guide to antiepileptic drugs • Tmax: 2–4 hours (oral ingestion); <4 hours (intramuscular adminis­ tration) • Time to steady state: 15–29 days (adults) • Pharmacokinetics: linear • Protein binding: 55% • Volume of distribution:  0.54 L/kg (adult volunteers); 0.61 L/kg (adult patients with epilepsy); ~1.0 L/kg (newborns) • Salivary concentrations: phenobarbital is secreted into saliva, and concentrations are similar to the unbound levels seen in plasma

Drug interaction profile

Metabolism: • Phenobarbital undergoes significant metabolism in the liver to two major metabolites, p-hydroxyphenobarbital (~20–30% of administered dose) which partially (50%) undergoes sequential metabolism to a glucuronic acid conjugate, and 9-D-glucopyranosylphenobarbital (~25–30% of administered dose), a nitrogen glucosidation conjugate • CYP2C9 plays a major role in the metabolism of phenobarbital to p-hydroxyphenobarbital with minor metabolism by CYP2C19 and CYP2E1 • The identity of the UGT enzyme responsible for the formation of 9-D-glucopyranosylphenobarbital is unknown • The metabolites of phenobarbital are not pharmacologically active • Phenobarbital undergoes autoinduction so that its clearance can increase and this may require an upward dosage adjustment when prescribed as monotherapy

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Elimination: • The elimination half-life is 70–140 hours (adults); 100–200 hours (newborn) • During the neonatal period, phenobarbital elimination accelerates markedly; thereafter, half-lives are very short, with average values of 63 hours during the first year of life and 69 hours between ages 1 and 5 years • Renal excretion:  ~20–25% of an administered dose is excreted unchanged in urine in adults, with large inter-individual variability Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on phenobarbital: –– Felbamate, oxcarbazepine, phenytoin, rufinamide, stiripentol, and valproic acid can decrease the clearance of phenobarbital and increase phenobarbital plasma levels • Interactions between AEDs: effects by phenobarbital: –– Phenobarbital can increase the clearance and decrease the levels of carbamazepine, clobazam, clonazepam, diazepam, ethosuximide,

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Phenobarbital

felbamate, lamotrigine, midazolam, oxcarbazepine, phenytoin, rufinamide, stiripentol, tiagabine, topiramate, valproic acid, and zonisamide • Interactions between AEDs and non-AED drugs:  effects on phenobarbital: –– Chloramphenicol, dicoumarol, and propoxyphene can increase phenobarbital plasma levels –– Phenobarbital absorption is significantly reduced by concurrent administration of antacids so that lower phenobarbital plasma levels are achieved • Interactions between AEDs and non-AED drugs:  effects by phenobarbital: –– Phenobarbital can increase the clearance and decrease the plasma levels of albendazole, alprazolam, alprenolol, 9-aminocampthotecin, amitriptyline, bupropion, citalopram, chlorpromazine, clomipramine, clozapine, cortisol, coumarin, cyclosporin, decipramine, desmethylchlomipramine, delavirdine, dicoumarol, docetaxel, doxepin, doxocycline, efavirenz, etoposide, felodipine, fentanyl, fluphenazine, griseofulvin, haloperidol, hydrocortisone, ifosfamide, imipramine, indinavir, itraconazole, ketoconazole, meperidine, methadone, methotrexate, methylprednisolone, metronidazole, mianserin, nefazodone, nelfinavir, nevirapine, nifedipine, nimodipine, nortriptaline, olanazapine, paclitaxel, paracetamol, paroxetine, prednisolone, procarbazine, propranolol, protriptyline, quetiapine, quinidine, risperidone, ritonavir, saquinavir, teniposide, theophylline, verapamil, vincristine, warfarin, zidovudine, and ziprasidone Pharmacodynamic drug interactions: • Phenobarbital can exacerbate the effects of alcohol and other CNS depressants Hormonal contraception: • Phenobarbital enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking phenobarbital

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Adverse effects How drug causes adverse effects: • Mechanism by which phenobarbital causes adverse effects has not been established and is presumed to be the same as the mechanism invoked for efficacy

the epilepsy prescriber’s guide to antiepileptic drugs Common adverse effects: • Sedation and drowsiness • Hyperactivity and irritability (especially in children) • Dysarthria, ataxia, in-coordination, nystagmus • Depression • Cognitive impairment • Decreased bone mineral density

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Life-threatening or dangerous adverse effects: • Very rare. Stevens-Johnson syndrome, erythema multiforme, toxic epidermal necrolysis • Hypersensitivity reactions, may lead to hepatic failure

Dosing and use

Rare and not life-threatening adverse effects: • Movement disorders, such as dyskinesia • Seizure exacerbation or de novo seizures • Hematologic toxicity, mainly megaloblastic anemia • Exacerbation of acute intermittent porphyria • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with phenobarbital; can be prevented by administration of vitamin K to the mother before delivery • Connective tissue disorders associated with long-term phenobarbital therapy (unusual in children), such as Dupuytren contractures, plantar fibromatosis, heel and knuckle pads, frozen shoulder, Peyronie disease, and diffuse joint pain • Loss of libido and erectile dysfunction Weight change: • Not common What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Dosage reduction in case of presumably dose-related adverse effects • CNS-related adverse effects are usually dose-dependent and are reversible • Many adverse effects disappear over time (usually within a few weeks) and include dizziness, sleepiness, drowsiness, tiredness, loss of appetite, nausea, and vomiting • Consider calcium and vitamin D supplements in case of decreased bone mineral density

Dosing and use Usual dosage range: • Adults and children over 12 years of age: 1.5–4 mg/kg/day

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• Children: –– Children (2 months to 1 year): 4–11 mg/kg per day –– Children (1 to 3 years): 3–7 mg/kg per day –– Children (3 to 6 years): 2–5 mg/kg per day • The initial loading dose of 15 to 20 mg/kg in newborns is similar to the dose in children and adults and will achieve a plasma level of approximately 20 mg/L (86.2 μmol/L); this level can usually be maintained in newborns with a maintenance dose of 3 to 4 mg/ kg per day

Phenobarbital

Available formulations: • Tablets: 15 mg, 30 mg, 32 mg, 60 mg, 65 mg, 100 mg • Solution: 20 mg/5 mL • Solution for intravenous injection: 60 mg/mL, 130 mg/mL, 200 mg/mL • Elixir: 15 mg/5 mL; 20 mg/5 mL How to dose: • For adults and children over 12 years of age:  start treatment with 1.5–4 mg/kg/day • Children:  start treatment with 2–11 mg/kg/day (2 months to 1 year: 4–11 mg/kg per day; 1 to 3 years: 3–7 mg/kg per day; 3 to 6 years: 2–5 mg/kg per day); doses above 11 mg/kg may be necessary in some infants to achieve high therapeutic levels • Because of the long elimination half-life and slow accumulation of phenobarbital, the full maintenance dose can be given on the first day; steady-state plasma levels will be reached only after 2–3 weeks • The intravenous loading dose of phenobarbital in the treatment of status epilepticus varies between 10 and 30 mg/kg; 15–20 mg/ kg is most common. The rate of administration should not exceed 100 mg/min (2 mg/kg/min in children weighing <40 kg) Dosing tips: • Given its long half-life, dividing the daily dose of phenobarbital into two or more doses, even in children, appears unnecessary • Salt formulations are more rapidly absorbed than are the acid formulations • The rate of absorption is increased if the sodium salt is ingested as a dilute solution or taken on an empty stomach

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How to withdraw drug: • May need to adjust dosage of concurrent medications as phenobarbital is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • After long-term administration, phenobarbital should always be discontinued gradually over several weeks

the epilepsy prescriber’s guide to antiepileptic drugs • Barbiturates and benzodiazepines are the antiepileptic drugs most commonly associated with withdrawal seizures upon rapid discontinuation • Unless there is a specific reason to proceed faster, it is appropriate to taper the phenobarbital dose linearly over 3 to 6 months, with reductions each 2–4 weeks

Dosing and use

Overdose: • The toxic dose of phenobarbital varies considerably; in general 1 g produces serious adverse effects and 2–10 g commonly results in death and are mostly secondary to cardiorespiratory failure • In individuals who have not been previously exposed to phenobarbital, plasma levels at or above 80 mg/L (345 μmol/L) are considered lethal; higher plasma levels may be tolerated by patients on chronic phenobarbital therapy • Symptoms include: constricted pupils, nystagmus, ataxia, somnolence, stupor or coma, pulmonary edema, and respiratory failure • Treatment consists mainly of cardiorespiratory support • Alkalinization with sodium bicarbonate, intravenous hydration and forced diuresis accelerate the elimination of phenobarbital through the kidneys • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes phenobarbital from blood and, therefore, serves as a useful procedure in cases of overdose

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Tests and therapeutic drug monitoring: • Monitoring of blood count and liver function tests usually not necessary • Consider vitamin D level and dual energy x-ray absorptiometry (DEXA) bone scan in patients at risk for osteopenia • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at phenobarbital plasma concentrations of 10–40 mg/L (43–172 μmol/L) –– The conversion factor from mg/L to μmol/L is 4.31 (i.e., 1 mg/L = 4.31 μmol/L) –– The reference range of phenobarbital in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Phenobarbital can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant Other warnings/precaution: • Phenobarbital may be habit forming • Tolerance and psychological and physical dependence may occur with long-term use

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• Should be prescribed with caution to patients with a history of mental depression, or suicidal tendencies, or a history of drug abuse Do not use: • In patients with known history of allergic reaction to barbiturates • In patients with known history of intermittent acute porphyria • Because the tablet formulation contains lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency, or glucose–galactose malabsorption should not take this formulation • If patient has a proven allergy to phenobarbital or to any of the excipients

Phenobarbital

Special populations Renal impairment: • Phenobarbital is renally secreted and thus the dose may need to be lowered in renally impaired patients • Because phenobarbital can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of phenobarbital Hepatic impairment: • Phenobarbital is extensively metabolized in the liver and consequently lower doses may be required Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults Elderly: • Elderly patients are more susceptible to adverse effects of phenobarbital (especially somnolence) and, therefore, often do better at lower doses • Because of an age-related reduction in renal and hepatic function, lower phenobarbital doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with phenobarbital is substantial

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Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding

the epilepsy prescriber’s guide to antiepileptic drugs

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Phenobarbital, overall role

an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Phenobarbital is classified by the US Food and Drug Administration as risk category D (positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy) • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Seizures, even mild seizures, may cause harm to the embryo/fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than phenobarbital monotherapy • Taper drug if discontinuing • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with phenobarbital; can be prevented by administration of vitamin K to the mother before delivery • During pregnancy phenobarbital pharmacokinetics change significantly so that in the first trimester total and free phenobarbital plasma concentrations decrease by 50–55% due to increased clearance and reduction in albumin concentrations; an increase in phenobarbital dose may be required in some patients Breast feeding • Breast milk: 30–50% of maternal plasma levels • Breastfed infants: phenobarbital plasma levels may reach 50–100% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects, including sedation, poor sucking and weight gain, and vomiting • If adverse effects are observed recommend bottle feed

The overall place of phenobarbital in the treatment of epilepsy Phenobarbital is a highly effective broad spectrum antiepileptic drug, being effective in all seizure types with the exception of absences. It is associated with rapid onset and prolonged action, and there is extensive experience of its use in adults and children and also in neonates for neonatal or febrile seizures. Phenobarbital has a significant role in the management of established status epilepticus, although it is usually the drug of third choice after a benzodiazepine and phenytoin. Because of its sedative and cognitive effects, it is never a drug of first choice, except for the treatment of neonatal seizures.

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Primary seizure types: • Partial and secondarily generalized seizures • Acute convulsive episodes and status epilepticus Secondary seizure types: • Prophylaxis of febrile seizures • Myoclonic seizures • Primarily generalized tonic–clonic seizures • Lennox-Gastaut syndrome

Phenobarbital

Potential advantages: • Broad spectrum of activity • Low systemic toxicity • Long half-life enabling once daily dosing • Can be administered intravenously and intramuscularly • Tolerance does not occur • Is effective in status epilepticus • Inexpensive Potential disadvantages: • Phenobarbital produces more sedative and behavioral adverse effects than most other antiepileptic drugs • Requires frequent blood testing and close monitoring • Associated with significant pharmacokinetic interactions and usually acts as an inducer of hepatic metabolism • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Boreus LO, Jalling B, Kallberg N. Phenobarbital metabolism in adults and in newborn infants. Acta Paediatrica Scandinavica 1978; 67: 193–200. Hirtz DG, Sulzbacher SI, Ellenberg JH, Nelson KB. Phenobarbital for febrile seizures–effects on intelligence and on seizure recurrence. New England Journal of Medicine 1990; 322: 364–369. Mattson RH, Cramer JA, Collins JF, Smith DB, Delgado-Escueta AV, Browne TR, Williamson PD, Treiman DM, McNamara JO, McCutchen CB. Comparison of carbamazepine, phenobarbital, phenytoin, and primidone in partial and secondarily generalized tonic-clonic seizures. New England Journal of Medicine 1985; 313: 145–151. Painter MJ, Scher MS, Stein AD, Armatti S, Wang Z, Gardiner JC, Paneth N, Minnigh B, Alvin J. Phenobarbital compared with 190

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phenytoin for the treatment of neonatal seizures. New England Journal of Medicine 1999; 341: 485–489. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Patsalos PN, Berry DJ, Bourgeois BFD, Cloyd JC, Glauser TA, Johannessen SI, Leppik IE, Tomson T, Perucca E. Antiepileptic drugs–Best practice guidelines for therapeutic drug monitoring: a position paper by the Subcommission on Therapeutic Drug Monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia 2008; 49: 1239–1276. Vining EP, Mellitis ED, Dorsen MM, Cataldo MF, Quaskey SA, Spielberg SP, Freeman JM. Psychologic and behavioral effects of antiepileptic drugs in children:  a double-blind comparison between phenobarbital and valproic acid. Pediatrics 1987; 80: 165–174. Wilensky AJ, Friel PN, Levy RH, Comfort CF, Kaluzny SP. Kinetics of phenobarbital in normal subjects and epileptic patients. European Journal of Clinical Pharmacology 1982; 23: 87–92. Wolf S, Forsythe A. Behavior disturbance, phenobarbital and febrile seizures. Pediatrics 1978; 61: 729–731.

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Phenytoin Therapeutics Chemical name and structure: Phenytoin, 5,5-diphenyl-2,4-imidazolidinedione, is a white powder, with a molecular weight of 252.26 for the free acid and a molecular weight of 274.25 for the sodium salt, which is equivalent to an acid content of 91.98%. It has an empirical formula of C15H12N2O2 . O

H N O

N H

Phenytoin

Brand names: • Aleviatin; Antisacer; Aurantin • Clerin; Cumatil • Di-Hydan; Difetoin; Dilantin; Dintoina; Diphantoine; Diphantoine Z; Diphedan; Ditoin; Ditomed • Epamin; Epanutin; Epilan-D; Epilantin; Epileptin; Epinat; Eptoin • Felantin; Fenatoin; Fenidantoin S; Fenitoina; Fenitoina Rubio; Fenitoina Sodica; Fenitron; Fenytoin; Fomiken • Hidanil; Hidantoína; Hydantin; Hydantol • Ikaphen • Kutoin • Lantidin; Lehydan • Movileps • Neosidantoina • Pepsytoin-100; Phenhydan; Phenilep; Phenytoin KP; Phenytoinum; Pyoredol • Sinergina • Utoin Generics available: • Yes

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Licensed indications for epilepsy: • Monotherapy or adjunctive therapy for patients of any age for the treatment of tonic–clonic seizures, focal seizures, or a combination of these, and for the treatment of seizures occurring during or following neurosurgery and/or severe head injury (UK-SPC) • Intravenous administration for the management of established status epilepticus (UK-SPC)

the epilepsy prescriber’s guide to antiepileptic drugs • Monotherapy or adjunctive therapy in adults and children (lower age not defined) with generalized tonic–clonic seizures and complex focal (psychomotor, temporal lobe) seizures, and prevention and treatment of seizures occurring during or following neurosurgery (FDA-PI)

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Licensed indications for non-epilepsy conditions: • Monotherapy for the treatment of trigeminal neuralgia in patients which have not responded to carbamazepine or in patients that are intolerant to carbamazepine (UK-SPC) Nonlicensed use for epilepsy: • There are none

Ineffective (contraindicated): • Phenytoin is contraindicated for absence seizures, myoclonic jerks, progressive myoclonic epilepsies such as Unverricht syndrome and probably in Lennox-Gastaut syndrome, and other childhood epileptic encephalopathies (although it may be effective in tonic seizures) Mechanism of action: • Acts as a use-dependent blocker of voltage-sensitive sodium channels • Interacts with the open channel conformation of voltage-sensitive sodium channels • Modulates sustained repetitive firing • Regulates calmodulin and second messenger systems • Inhibits calcium channels and calcium sequestration

Pharmacokinetics

Nonlicensed use for non-epilepsy conditions: • Arrhythmias

Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 4 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If phenytoin is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Pharmacokinetics Absorption and distribution: • Oral bioavailability: ≥ 80% (bioavailability is formulation dependent) • Food co-ingestion:  nasogastric feeding and co-ingestion of certain foods can reduce phenytoin absorption from the gastrointestinal tract • Tmax: 1–12 hours (rate of absorption is formulation dependent)

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Phenytoin 194

• Time to steady state: 6–21 days • Pharmacokinetics:  nonlinear due to saturable metabolism so that clearance decreases with increasing dose • Protein binding: 90% • Volume of distribution: 0.5–0.8 L/kg • Salivary concentrations: phenytoin is secreted into saliva and concentrations are similar to the unbound levels seen in plasma Metabolism: • Phenytoin undergoes extensive metabolism in the liver by hydroxylation to various metabolites, the principal metabolites being 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH; 67–88%) and a dihydrodiol derivative (7–11%) • The isoenzymes responsible for the hydroxylation of phenytoin are CYP2C9 (~80%) and CYP2C19 (~20%) • In excess of 60% of pHPPH is subsequently glucuronidated and excreted in urine • The metabolites of phenytoin are not pharmacologically active • Phenytoin undergoes autoinduction, primarily by means of CYP2C19, so that its clearance can increase, and this may require an upward dosage adjustment when prescribed as monotherapy Elimination: • In the absence of enzyme-inducing AEDs, half-life values for phenytoin are 30–100 hours • In the presence of enzyme-inducing co-medication, half-life values for phenytoin are 30–100 hours • Phenytoin elimination is not first-order and, therefore, half-life values increase with increasing plasma concentrations • Renal excretion:  ~5% of an administered dose is excreted as unchanged phenytoin in urine

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on phenytoin: –– Carbamazepine and phenobarbital can increase the clearance of phenytoin and decrease phenytoin plasma levels –– Carbamazepine, clobazam, felbamate, oxcarbazepine, phenobarbital, rufinamide, stiripentol, topiramate, and zonisamide can decrease the clearance of phenytoin and increase phenytoin plasma levels –– Vigabatrin can decrease phenytoin plasma levels by means of an unknown mechanism –– Valproic acid can increase the free fraction of phenytoin by displacing phenytoin from its plasma protein (albumin) binding site and a concurrent inhibition of phenytoin clearance

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Pharmacodynamic drug interactions: • To date, none have been reported

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Drug interaction profile

• Interactions between AEDs: effects by phenytoin: –– Phenytoin can decrease plasma levels of carbamazepine, clobazam, clonazepam, ethosuximide, felbamate, lamotrigine, oxcarbazepine, phenobarbital, primidone, rufinamide, stiripentol, tiagabine, topiramate, valproic acid, and zonisamide • Interactions between AEDs and non-AED drugs:  effects on phenytoin: –– Allopurinol, amiodarone, azapropazone, bleomycin, chlorphenamine, clarithromycin, chloramphenicol, cimetidine, clinafloxacin, cotrimoxazole, disulfiram, dextropropoxyphene (propoxyphene), dicoumarol, diltiazem, doxifluridine, erythromycin, esomeprazole, fenyramidol, fluconazole, 5-fluorouracil, fluoxetine, fluvoxamine, imipramine, indinavir, isoniazid, itraconazole, methylphenidate, metronidazole, miconazole, nelfinavir, nifedipine, omeprazole, risperidone, ritonavir, saquinavir, sertraline, sulfinpyrazone, tamoxifen, tegafur, ticlopidine, trazodone, verapamil, viloxazine, and voriconazole can increase phenytoin plasma levels –– Antacids, acyclovir, carboplatin, carmustine, cisplatin, dexa­ methasone, diazoxide, etoposide, loxapine, methotrexate, rifampicin, St. John’s wort, sucralfate, theophylline, and vinblastine can decrease phenytoin plasma levels –– Phenylbutazole, salicylates, and tolbutamide can increase the free fraction of phenytoin by displacing phenytoin from its plasma protein (albumin) binding site and a concurrent inhibition of phenytoin clearance • Interactions between AEDs and non-AED drugs:  effects by phenytoin: –– Phenytoin can decrease plasma levels of albendazole, 9-amino­ campthotecin, amiodarone, amitriptyline, bupropion, busulphan, citalopram, clomipramine, clozipine, cortisol, cyclophosphamide, cyclosporin, delavirdine, desipramine, desmethylclomipramine, dexamethasone, dicoumarol, disopyramide, digoxin, docetaxel, doxycycline, efavirenz, erythromycin, etoposide, felodipine, fentanyl, fluphenazine, haloperidol, hydrocortisone, ifofosfamide, imipramine, indinavir, irinotecan, itraconazole, ketoconazole, mebendazole, meperidine, methadone, methotrexate, methylprednisolone, mexiletine, mianserin, mirtazapine, nefazodone, nelfinavir, nevirapine, nimodipine, nisoldipine, nortriptyline, olanzapine, paclitaxel, paracetamol, paroxetine, pethidine, praziquantel, prednisolone, procarbazine, protriptyline, quetiapine, quinidine, risperidone, ritonavir, saquinavir, sirolimus, tacrolimus, teniposide, theophylline, thioridazine, topotecan, verapamil, vincristine, voriconazole, zidovudine, and ziprasidone –– Phenytoin can increase plasma levels of chloramphenicol

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Hormonal contraception: • Phenytoin enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking phenytoin Adverse effects How drug causes adverse effects: • CNS adverse effects theoretically due to excessive actions at ­voltage-sensitive sodium channels • Rash hypothetically an allergic reaction

Phenytoin

Common adverse effects: • Ataxia, nystagmus, slurred speech, decreased coordination, mental confusion • Paresthesia, drowsiness, vertigo, dizziness, insomnia, headache • Nausea, vomiting, constipation • Toxic hepatitis, liver damage • Gingival hyperplasia, hirsutism, dysmorphism, hypertrichosis Life-threatening or dangerous adverse effects: • Rare serious rash including Stevens-Johnson syndrome and toxic epidermal necrolysis (Lyell syndrome) can occur • Lymphadenopathy, including benign lymph node hyperplasia, pseudolymphoma, lymphoma, and Hodgkin disease • Rare hematological abnormalities, some fatal, have been associated with phenytoin and these include leukopenia, anemia, thrombocytopenia, agranulocytosis, pancytopenia, with and without bone marrow suppression, and aplastic anemia • Occasionally macrocytosis and megaloblastic anemia have occurred but these usually respond to folic acid therapy • Phenytoin may be associated with an increased risk of suicidal ideation and patients should be monitored for such behavior • Cerebella dysfunction (irreversible) • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with phenytoin; can be prevented by administration of vitamin K to the mother before delivery Rare and not life-threatening adverse effects: • Movement disorders such as chorea, dystonia, tremor, and asterixis • Hypoglycemia • Confusional states such as delirium, psychosis, or encephalopathy

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Weight change: • Not common, reported but not expected

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Dosing and use Usual dosage range: • Adults: 200–400 mg/day • Children: 5–10 mg/kg/day

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Dosing and use

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Dosage reduction in case of presumably dose-related adverse effects • Risk of serious adverse effects is greatest in the first few months of treatment • If patient develops signs of a rash, phenytoin should be discontinued and patient should be monitored and investigated for organ involvement (hepatic, renal, hematological) • If the rash is of the severe type (Stevens-Johnson syndrome or Lyell syndrome) the drug should not be resumed; if the rash is of the milder type (measles-type or scarlatiniform), phenytoin may be resumed after the rash has completely disappeared; if the rash recurs upon reinstituting phenytoin, further phenytoin medication is contraindicated

Available formulations: • Capsules: 25 mg, 50 mg, 100 mg, 300 mg • Infatabs chewable tablets: 50 mg • Oral suspension: 30 mg/5 mL • Parenteral solution: 250 mg/5 mL How to dose: • When initiating phenytoin treatment start with a low dose and titrate slowly so as to minimize adverse effects –– For adults: start treatment with 150–300 mg/day either as a single dose (nocte) or in two equally divided doses; every 3–4 weeks increase by up to 50 mg/day in divided doses; maintenance dose generally 200–400 mg/day; some patients may require up to 500 mg/day –– Children: start treatment with 5 mg/kg/day either as a single dose (nocte) or in two equally divided doses; every 3–4 weeks increase by up to 5 mg/kg/day in divided doses; maintenance dose generally 5–10 mg/kg/day; some patients may require up to 300 mg/ day –– Neonates:  because phenytoin absorption is unreliable after oral ingestion, a loading dose of 15–20 mg/kg of the parenteral solution will usually produce plasma levels within the generally accepted therapeutic range; maintenance dose may be >10 mg/kg/day

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–– For status epilepticus: the usual preparation for emergency treatment is a 5 mL ampule containing 250 mg phenytoin. For the treatment of established status epilepticus, the rate of infusion should not exceed 50 mg/min (to avoid hypotension) and it is prudent to reduce this to 20–30 mg/min in the elderly and to < 25 mg/min in children – the usual dose for adults is approximately 1000 mg, therefore, taking approximately 20 minutes to administer; phenytoin is constituted in propylene glycol (40%), ethanol (10%), and water (250 mg in 5 mL)

Phenytoin

Dosing tips: • Because of the nonlinear pharmacokinetics of phenytoin, and the fact that nonlinearity occurs at different doses for different patients, there is wide inter-patient variability in phenytoin plasma levels with equivalent doses and, therefore, dosing should be accompanied by regular checks on phenytoin plasma levels • Dosage changes should not be undertaken at intervals shorter than 7–10 days; typically the interval should be 3–4 weeks • Epanutin capsules contain phenytoin sodium whereas Epanutin suspension and Epanutin infatabs contain phenytoin; although 100 mg of phenytoin sodium is equivalent to 92 mg of phenytoin on a molecular basis, these molecular equivalents are not necessarily biologically equivalent and care needs to be exercised where it is necessary to change the dosage form and plasma level monitoring is recommended • Epanutin infatabs may be chewed • Parenteral infusion solution should not be added to drip bottles or mixed with other drugs because of serious risk of precipitation; administration by means of a side arm or directly using an infusion pump is preferable • Intramuscular administration should not be used in the treatment of status epilepticus because the attainment of peak phenytoin plasma levels may require up to 24 hours How to withdraw drug: • May need to adjust dosage of concurrent medications as phenytoin is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper:  a gradual dose reduction over a period of many weeks should be undertaken • Rapid discontinuation may induce withdrawal seizures and should only be undertaken if there are safety concerns (e.g., a rash with serious characteristics)

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Overdose: • The mean lethal dose for adults is considered to be 2–5 g; the lethal dose in children is unknown

the epilepsy prescriber’s guide to antiepileptic drugs • Initial symptoms include ataxia, nystagmus, and dysarthria; subsequently the patient becomes comatose, the pupils are unresponsive, and hypotension occurs followed by respiratory depression and apnea; death is the consequence of respiratory and circulatory depression • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes phenytoin from blood and, therefore, serves as a useful procedure in cases of overdose

Other warnings/precautions: • Life-threatening rashes have developed in association with phenytoin use; phenytoin should generally be discontinued at the first sign of serious rash • Caution is required when treating patients with a history of allergy or rash to other antiepileptic drugs • Phenytoin therapy may interfere with vitamin D metabolism and in the absence of an adequate dietary intake of vitamin D or exposure to sunlight, osteomalacia, hypocalcemia or rickets may develop • Because phenytoin exacerbates porphyria, caution should be exercised in patients suffering from this disorder • An effect on glucose metabolism, inhibition of insulin release, and hyperglycemia may occur, particularly at high phenytoin levels

Dosing and use

Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests • During treatment: liver and kidney function tests every 12 months; folate levels should be monitored every 6 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at plasma phenytoin concentrations of 10–20 mg/L (40–80 μmol/L) –– The conversion factor from mg/L to μmol/L is 3.96 (i.e., 1 mg/L = 3.96 μmol/L) –– In clinical settings whereby the phenytoin free fraction is changed (e.g., by drugs [valproic acid, phenylbutazole, salicylates, and tolbutamide] that act as protein binding displacers or by pathologies associated with reduced albumin concentrations [children, elderly, pregnancy, renal and hepatic disease, malnutrition, and after surgery]), patient management is best guided by use of phenytoin free nonprotein bound plasma concentrations –– The reference range of phenytoin in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Phenytoin can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant

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• Lowers calcium and folic acid blood levels: folic acid supplementation may be necessary • Plasma levels of phenytoin sustained above the optimum range may result in confusional states referred to as “delirium,” “psychosis,” or “encephalopathy,” or rarely irreversible cerebella dysfunction • Parenteral phenytoin should not be administered by intramuscular injection because the medication will crystallize within muscles and cause significant pain • Intravenous administration should be accompanied by continuous monitoring of the electrocardiogram and of blood pressure and respiratory depression; cardiac resuscitation equipment should be available

Phenytoin

Do not use: • If patient has a proven allergy to phenytoin or to any of the excipients • Because formulations contains lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency, or glucose–galactose malabsorption should not take this medicine

Special populations Renal impairment: • Phenytoin is renally secreted and thus the dose may need to be lowered in renally impaired patients • Because phenytoin can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of phenytoin Hepatic impairment: • Phenytoin is extensively metabolized and consequently lower doses will be required in patients with hepatic impairment Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults • The absorption of phenytoin following oral absorption in neonates is unpredictable and phenytoin metabolism is depressed; it is particularly important to monitor plasma levels in neonates

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Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in hepatic and renal function, lower phenytoin doses are appropriate

the epilepsy prescriber’s guide to antiepileptic drugs • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the possibility of pharmacokinetic interactions with phenytoin is particularly high • Because of a tendency for lower serum albumin values, elderly patients may have a higher free (unbound) fraction of phenytoin

Phenytoin, overall role

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Phenytoin is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than phenytoin monotherapy • Taper drug if discontinuing • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with phenytoin; can be prevented by administration of vitamin K to the mother before delivery • Seizures, even mild seizures, may cause harm to the embryo/fetus • During pregnancy phenytoin pharmacokinetics change significantly so that phenytoin plasma concentrations decrease by 39–56% and free phenytoin plasma concentrations decrease by 31–82% due to increased clearance consequent to enhanced hydroxylation and also due to reduced gastrointestinal absorption; an increase in phenytoin dose may be required in some patients

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Breast feeding • Breast milk: 10–60% of maternal plasma levels • Breastfed infants:  phenytoin plasma levels are <10% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (irritability or sedation) • If adverse effects are observed recommend bottle feed

The overall place of phenytoin in the treatment of epilepsy Phenytoin, an antiepileptic drug that continues to be widely used, is highly effective in focal seizures and generalized tonic–clonic

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seizures, and to date no other antiepileptic drug has been shown to be more effective in this regard. However, its adverse effects and its complicated pharmacokinetic characteristics hinder its use. If phenobarbital fails, phenytoin is very useful in neonatal seizures. Phenytoin is often considered the drug of choice for the management of established status epilepticus. Primary seizure types: • Partial seizures • Generalized tonic–clonic seizures Secondary seizure types: • None

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Potential advantages: • No other antiepileptic drug has been shown to have superior efficacy (partial and generalized tonic–clonic seizures) in randomized controlled trials Potential disadvantages: • Associated with nonlinear pharmacokinetics so that plasma levels increase disproportionately to dose and dosing can only be undertaken with guidance of therapeutic drug monitoring (measurement of blood levels) • Associated with more pharmacokinetic interactions than any other antiepileptic drug, and usually acts as an inducer of hepatic metabolism • Long-term use of phenytoin in women is unsuitable because of aesthetic adverse effects • Potential teratogen

Suggested reading de Silva M, MacArdle B, McGowan M, Hughes E, Stewart J, Neville BG, Johnson AL, Reynolds EH. Randomized comparative monotherapy trial of phenobarbitone, phenytoin, carbamazepine or sodium valproate for newly diagnosed childhood epilepsy. Lancet 1996; 347: 709–713. Heller AJ, Chesterman P, Elwes RD, Crawford P, Chadwick D, Johnson AL, Reynolds EH. Phenobarbitone, phenytoin, carbamazepine, or sodium valproate for newly diagnosed epilepsy: a randomised comparative monotherapy trial. Journal of Neurology Neurosurgery, and Psychiatry 1995; 58: 44–50. Mattson RH, Cramer JA, Collins JF, Smith DB, Delgado-Escueta AV, Browne TR, Williamson PD, Treiman DM, McNamara JO, McCutchen CB. Comparison of carbamazepine, phenobarbital, phenytoin and primidone in partial and secondarily generalized

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tonic-clonic seizures. New England Journal of Medicine 1985; 313: 145–151. Patsalos PN, Berry DJ, Bourgeois BF, Cloyd JC, Glauser TA, Johannessen SI, Leppik IE, Tomson T, Perucca E. Antiepileptic drugs  – Best practice guidelines for therapeutic drug monitoring: a position paper by the Subcommission on Therapeutic Drug Monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia 2008; 49: 1239–1276. Patsalos PN, Froscher W, Pisani F, van Rijn CM. The importance of drug interactions in epilepsy therapy. Epilepsia 2002; 43: 365–385. Patsalos PN, Perucca E. Clinically important interactions in epilepsy:  general features and interactions between antiepileptic drugs. Lancet Neurology 2003; 2: 347–356. Patsalos PN, Perucca E. Clinically important interactions in epilepsy: interactions between antiepileptic drugs and other drugs. Lancet Neurology 2003; 2: 473–481. Reynolds EH. Chronic antiepileptic drug toxicity: a review. Epilepsia 1975; 16: 319–352.

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Piracetam Therapeutics Chemical name and structure: Piracetam, 2-oxo-1-pyrrolidine acetamide, is a white powder, with a molecular weight of 142.2 and an empirical formula of C6H10N2O2 .

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H2 N

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O Brand names: • Acetar; Avigilen; Axonyl • Braintop • Cerebroforte; Cerebropan; Cerebrosteril; Cerebryl; Cerepar N; Cetam; Ciclofalina; Cintilan; Cleveral; Cuxabrain • Dinagen; Docpirace • Encefalux; Encetrop • Flavis • Gabacet; Genogris; Geram; Geratam • Huberdasen • Kalicor • Lucetam; Lytenur • Merapiran; Myocalm • Neuronova; Noodis; Noostan; Nootron; Nootrop; Nootropicon; Nootropil; Nootropyl; Normabrain; Norzetam; Novocephal • Oikamid • Pirabene; Piracebral; Piracemed; Piracetam AbZ; Piracetam AL; Piracetam EG; Piracetam Faro; Piracetam Heumann; Piracetam Interpharm; Piracetam Prodes; Piracetam Stada; Piracetam Verla; Piracetam von ct; Piracetam Elbe-Med; Piracetam-Farmatrading; Piracetam-neuraxpharm; Piracetam-ratiopharm; Piracetam-RPh; Piracetop; Piracetrop; Pirax; Pirazetam-Eurogenerics; Psycoton; Pyramen • Qropi • Sinapsan; Stimubral; Synaptine

the epilepsy prescriber’s guide to antiepileptic drugs Generics available: • Yes

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Licensed indications for epilepsy: • Adjunctive treatment of myoclonus of cortical origin irrespective of etiology (UK-SPC) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • There are none

Ineffective (contraindicated): • There is some evidence to suggest that piracetam may aggravate seizures in some patients

Pharmacokinetics

Nonlicensed use for non-epilepsy conditions: • Anti-aging agent • Clotting, coagulation and vasospastic disorders • Cognitive enhancer:  particularly after stroke and in chronic ischemia • Treatment of alcoholism • Verbal memory enhancer

Mechanism of action: • Although disturbances of serotonergic and GABA-ergic function are implicated in cortical myoclonus, piracetam does not seem to modify these systems and, therefore, its mechanism of action is unknown • Actions associated with piracetam include:  enhancement of oxidative glycolysis, anticholinergic effects, increases cerebral blood flow, reduces platelet aggregation, and improves erythrocyte function; however, as to how these properties contribute to the suppression of myoclonus is unclear Efficacy profile: • The goal of treatment is complete remission of seizures • Often the effects of piracetam are immediate, profound and longterm in that tolerance does not develop. • Discontinuation should occur in the absence of definitive, meaningful seizure reduction

Pharmacokinetics Absorption and distribution: • Oral bioavailability: ~100% • Food co-ingestion:  neither delays the rate of absorption nor decreases the extent of absorption

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• Tmax: 0.5–1.5 hours • Time to steady state: 1–2 days • Pharmacokinetics: linear • Protein binding: 0% • Volume of distribution: 0.6 L/kg • Salivary concentrations:  it is not known whether piracetam is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma Metabolism: • Piracetam is not metabolized Elimination: • Following a single dose, half-life values in young men are 4–6 hours • Renal excretion:  ~100% of an administered dose is excreted unchanged in urine

Piracetam 206

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on piracetam: –– To date, there have been no reports of AEDs affecting the clearance of piracetam and affecting piracetam plasma levels • Interactions between AEDs: effects by piracetam: –– To date, there have been no reports of piracetam affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on piracetam: –– To date, there have been no reports of other non-AED drugs affecting the clearance of piracetam and affecting piracetam plasma levels • Interactions between AEDs and non-AED drugs:  effects by piracetam: –– To date, there have been no reports of piracetam affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • In combination with clonazepam, piracetam may be particularly efficacious in suppressing myoclonic seizures • In combination with acenocoumarol, piracetam can significantly decrease platelet aggregation, β-thromboglobulin release, levels of fibrinogen and von Willebrand factors, and whole blood and plasma viscosity • Confusion, irritability, and sleep disorders have been reported in a patient administered with thyroid extract (T3 + T4) and piracetam

the epilepsy prescriber’s guide to antiepileptic drugs Hormonal contraception: • Piracetam is not expected to affect the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, should not compromise contraception control

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Adverse effects How drug causes adverse effects: • Unknown Common adverse effects: • Dizziness, insomnia • Nausea, gastrointestinal discomfort • Agitation, anxiety, confusion, hallucination

Rare and not life-threatening adverse effects: • Asthenia • Depression • Somnolence

Dosing and use

Life-threatening or dangerous adverse effects: • Anaphylactic reaction, hypersensitivity • Rare rash may occur

Weight change: • Weight gain is common What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Typically adverse effects are mild and transient • If necessary reduce piracetam dose

Dosing and use Usual dosage range: • Adults: up to 20 g/day • Children <16 years of age: not recommended Available formulations: • Tablets: 800 mg, 1200 mg • Solution (300 mL): 333.3 mg/mL How to dose: • When initiating piracetam treatment start with a low dose and titrate slowly so as to minimize adverse effects

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–– For adults: start treatment with 7.2 g per day in two–three divided doses; each 3–4 days increase by 4.8 g daily; maintenance dose generally < 20 g/day given in two or three equally divided doses Dosing tips: • The solution formulation can be used in patients who have difficulty swallowing and after ingestion should be followed by water or a soft drink to reduce the bitter taste of piracetam solution • At the higher doses the major drawback is the number of tablets that need to be taken and their bulk, although drowsiness is occasionally dose-limiting at the high dose range

Piracetam

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as piracetam is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Taper: a gradual dose reduction over a 1- to 3-week period should be undertaken • Rapid discontinuation may induce myoclonic or generalized seizures Overdose: • No specific measures are indicated; to date, no fatalities have been reported • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes piracetam from blood and, therefore, may be a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Before starting: coagulation tests, liver and kidney function tests • During treatment:  coagulation tests, liver and kidney function tests every 6–12 months • Therapeutic drug monitoring: –– There are no data relating the plasma concentration of piracetam with that of seizure suppression –– Thus, although routine monitoring of piracetam is not recommended, measurement of plasma piracetam concentrations may be useful as a check on compliance –– There are no data indicating the usefulness of monitoring piracetam by use of saliva

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Other warnings/precautions: • Due to the effect of piracetam on platelet aggregation, caution is recommended in patients with underlying disorders of hemostasis, major surgery or sever hemorrhage • Some patients may experience hyperkinesia, somnolence, nervous­ ness, and depression and thus caution needs to be exercised if patient intends to drive or use machinery

the epilepsy prescriber’s guide to antiepileptic drugs Do not use: • If patient has severe renal (CrCl of <20 mL/min) or hepatic impairment • If patient has a cerebral hemorrhage • If patient has a proven allergy to piracetam, other pyrrolidone derivatives, or to any of the excipients

Hepatic impairment: • Even though piracetam is not metabolized, its use is contraindicated in hepatically impaired patients

Special populations

Special populations Renal impairment: • Piracetam is renally excreted, so the dose needs to be lowered: recommended adjustments are: –– Mild renal impairment (CrCl of 50–79 mL/min)  – 2/3 usual daily dose –– Moderate impairment (CrCl of 30–49 mL/min)  – 1/3 usual daily dose –– Severe impairment (CrCl of 20–30 mL/min) – 1/6 usual daily dose • Because piracetam can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of piracetam

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Children: • Piracetam is not licensed for use in children Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal function, lower piracetam doses are appropriate and should be based on creatinine clearance values Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Piracetam is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans]

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• Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than piracetam monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • There are no available data on the pharmacokinetic changes of piracetam during pregnancy Breast feeding • Breast milk: it is not known how much is excreted in breast milk • Breastfed infants: it is not known what plasma piracetam concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

Piracetam

The overall place of piracetam in the treatment of epilepsy Cortical myoclonus, with or without epilepsy, can result in profound disability. The jerks are often exacerbated by action, and the patient may be bed bound and immobile, unable to move without severe myoclonic jerking disrupting all motor activity. Piracetam is particularly effective for the treatment of myoclonic seizures and often its effects are immediate, profound, and long-term in that tolerance does not develop. Furthermore, in some cases, piracetam can have a truly remarkable effect, suppressing the myoclonus and reversing completely even severe disability. Piracetam is the only drug that improves the myoclonus in some patients with progressive myoclonic epilepsy syndromes. Primary seizure types: • Myoclonic seizures Secondary seizure types: • None

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Potential advantages: • Piracetam is by far the best antiepileptic drug for the treatment of cortical myoclonus and its associated profound disability • It is well-tolerated and is associated with very few adverse effects which are typically mild and transient • Because it is excreted exclusively by renal elimination, piracetam is not associated with any significant pharmacokinetic interactions

the epilepsy prescriber’s guide to antiepileptic drugs Potential disadvantages: • Not effective in many cases of cortical myoclonus • Bulky tablets which have to be ingested in large numbers (particularly at the higher doses) • Potential teratogen, but not more than most other antiepileptic drugs

Piracetam, overall role

Suggested reading Brown P, Steiger MJ, Thompson PD, Rothwell JC, Day BL, Salama M, Waegemans T, Marsden CD. Effectiveness of piracetam in cortical myoclonus. Movement Disorders 1993; 8: 63–68. Koskiniemi M, van Vleyman B, Hakamies L, Lamusuo S, Taalas J. Piracetam relieves symptoms in progressive myoclonic epilepsy: a multicentre, randomised, double-blind, crossover study comparing the efficacy and safety of three dosages of oral piracetam with placebo. Journal of Neurology, Neurosurgery, and Psychiatry 1998; 64: 344–348. Obeso JA, Artieda J, Quinn N, Rothwell JC, Luquin MR, Vaamonde J, Marsden CD. Piracetam in the treatment of different types of myoclonus. Clinical Neuropharmacology 1988; 11: 529–536. Shorvon SD. Pyrrolidine derivatives. Lancet 2001; 358: 1885–1892.

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Pregabalin Therapeutics Chemical name and structure: Pregabalin, S-3-(aminomethyl)-5-methylhexanoic acid, is a white powder, with a molecular weight of 159.2 and an empirical formula of C9H17NO2 .

H2N

OH

* H O

Brand names: • Lyrica

Pregabalin

Generics available: • No Licensed indications for epilepsy: • Adjunctive treatment of partial seizures with or without secondary generalization in adults (UK-SPC, FDA-PI ) Licensed indications for non-epilepsy conditions: • Peripheral and central neuropathic pain (UK-SPC) • Generalized anxiety disorders (UK-SPC) • Management of pain associated with diabetic peripheral neuro­ pathy (FDA-PI) • Management of postherpetic neuralgia (FDA-PI) • Management of fibromyalgia (FDA-PI) Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • Panic disorder • Social anxiety disorder

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Ineffective (contraindicated): • There is some evidence to suggest that pregabalin may exaggerate myoclonus • Treatment-emergent myoclonic jerks, even in patients with focal seizures, may be a warning sign against the use of pregabalin in generalized and other myoclonic epilepsies where myoclonus is often prominent

the epilepsy prescriber’s guide to antiepileptic drugs Mechanism of action: • Binds to the α2-δ protein subunit of voltage-gated calcium channels • This closes N and P/Q presynaptic calcium channels, diminishing excessive neuronal activity and neurotransmitter release • Although structurally related to GABA, it does not directly act on GABA or its receptors

Pharmacokinetics Absorption and distribution: • Oral bioavailability: ≥90% • Food co-ingestion:  decreases the extent of absorption (25–30%) and absorption is delayed by ~2.5 hours • As a leucine analog, pregabalin is transported both into the blood from the gut and also across the blood–brain barrier into the brain from the blood by the system L transport system (a sodium independent transporter) as well as by additional sodiumdependent amino acid transporter systems • Tmax: 1–2 hours • Time to steady state: 1–2 days • Pharmacokinetics: linear • Protein binding: 0% • Volume of distribution: 0.57 L/kg • Salivary concentrations:  it is not known whether pregabalin is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

Pharmacokinetics

Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 2 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If pregabalin is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Metabolism: • Pregabalin is not metabolized Elimination: • Following a single dose, half-life values are 5–7 hours • The renal clearance of pregabalin is proportional to the creatinine clearance • Renal excretion: ~98% of an administered dose is excreted unchanged in urine

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Pregabalin

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on pregabalin: –– To date, there have been no reports of AEDs affecting the clearance of pregabalin and affecting pregabalin plasma levels • Interactions between AEDs: effects by pregabalin: –– To date, there have been no reports of pregabalin affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on pregabalin: –– To date, there have been no reports of other non-AED drugs affecting the clearance of pregabalin and affecting pregabalin plasma levels • Interactions between AEDs and non-AED drugs:  effects by pregabalin: –– To date, there have been no reports of pregabalin affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • Pregabalin may potentiate the effects of ethanol and lorazepam • Respiratory failure and coma has been reported in patients coprescribed pregabalin and other CNS depressant medications • Pregabalin appears to be additive in the impairment of cognitive and gross motor function associated with oxycodone • CNS adverse effects, particularly somnolence, can increase in patients co-prescribed anti-spasticity agents Hormonal contraception: • Pregabalin does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects How drug causes adverse effects: • CNS adverse effects may be due to excessive blockade of voltagesensitive calcium channels

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Common adverse effects: • Somnolence, dizziness • Ataxia, fatigue, tremor, dysarthria, paresthesia, abnormal coordination • Impaired attention, memory impairment, confusion, euphoric mood, irritability • Vomiting, dry mouth, constipation, increased appetite, flatulence • Blurred vision, diplopia

the epilepsy prescriber’s guide to antiepileptic drugs • Peripheral edema • Libido decreased, erectile dysfunction

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Life-threatening or dangerous adverse effects: • Rare neutropenia, hypoglycemia, atrioventricular block and congestive heart failure • Some patients may experience hypersensitivity reactions, including facial, perioral and upper airway angioedema  – pregabalin should be withdrawn immediately if these symptoms present • Cases of renal failure have been reported, however, discontinu­ ation of pregabalin reversed the adverse effect

Weight change: • Weight gain is common

Dosing and use

Rare and not life-threatening adverse effects: • Ageusia • Amenorrhea, dysmenorrhea • Ascitis, dysphagia, pancreatitis • Hyporeflexia, hyperesthesia • Hyperacusis • Myoclonus, dyskinesia • Peripheral vision loss, oscillopsia, photopsia, strabismus • Syncope, stupor

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Sedation is dose-related and can subside with time • Take more of the dose at night to reduce daytime sedation • Lower the dose

Dosing and use Usual dosage range: • Adults: 150–600 mg/day Available formulations: • Capsules: 25 mg, 50 mg, 75 mg, 100 mg, 150 mg, 200 mg, 225 mg, 300 mg How to dose: • When initiating pregabalin treatment start with a low dose and titrate slowly so as to minimize adverse effects. –– For adults: start treatment with 50 mg/day in two divided doses; subsequently at 7-day intervals increase in steps of 50 mg daily

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to 300 mg daily in two to three divided doses; maintenance dose generally not greater than 600 g/day given in two or three equally divided doses Dosing tips: • Titration of dose should be undertaken based on individual tolerability and response to the drug • Patients should be informed that in the event of the need to withdraw pregabalin they may experience a variety of withdrawal symptoms (insomnia, headache, nausea, diarrhea, flu syndrome, nervousness, depression, pain, sweating, and dizziness)

Pregabalin

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as pregabalin is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Taper:  a gradual dose reduction over a minimum of a 1-week period should be undertaken • Withdrawal may be associated with a variety of symptoms including: insomnia, headache, nausea, diarrhea, flu syndrome, nervousness, depression, pain, sweating, and dizziness • Rapid discontinuation may induce withdrawal seizures Overdose: • In overdoses up to 15 g, no unexpected adverse effects were observed • The most common adverse effects observed with pregabalin overdose include somnolence, confusional state, agitation, and restlessness • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes pregabalin from blood (50% over 4 hours) and, therefore, may be a useful procedure in cases of overdose

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Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests • During treatment:  liver and kidney function tests every 6–12 months • Therapeutic drug monitoring: –– There are no data relating the plasma concentration of pregabalin with that of seizure suppression –– Thus, although routine monitoring of pregabalin is not recommended, measurement of plasma pregabalin concentrations may be useful as a check on compliance –– There are no data indicating the usefulness of monitoring pregabalin by use of saliva • Before giving a drug that can cause weight gain to an overweight or obese patient, consider determining whether the patient already has prediabetes (fasting plasma glucose 100–125 mg/dL), diabetes (fasting plasma glucose greater than 126 mg/dL), or dyslipidemia

the epilepsy prescriber’s guide to antiepileptic drugs (increased total cholesterol, LDL cholesterol, and triglycerides; decreased HDL cholesterol), and treat or refer such patients for treatment, including nutrition and weight management, physical activity counseling, smoking cessation, and medical management • Monitor weight and BMI during treatment

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Other warnings/precautions: • Some diabetic patients who gain weight on pregabalin treatment may need to adjust their hypoglycemic medications • Some patients may experience dizziness and somnolence and thus caution needs to be exercised if patient intends to drive or use machinery

Special populations Renal impairment: • Pregabalin is renally excreted, so the dose needs to be adjusted according to creatinine clearance as follows: –– CrCL of ≥ 60 mL/min – starting dose: 150 mg/day taken twice or three times a day; maximum dose: 600 mg/day –– CrCL of ≥30-<60 mL/min  – starting dose:  75 mg/day taken twice or three times a day; maximum dose: 300 mg/day –– CrCL of ≥15-<30 mL/min – starting dose: 25–50 mg/day taken once or twice a day; maximum dose: 150 mg/day –– CrCL of <15 mL/min – starting dose: 25 mg/day taken once a day; maximum dose: 75 mg/day • Because pregabalin can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of pregabalin

Special populations

Do not use: • If patient has a proven allergy to pregabalin or gabapentin or to any of the excipients – tablets contain lactose • Because the tablets contain lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency, or ­g lucose –galactose malabsorption should not take this formulation

Hepatic impairment: • Because pregabalin is not metabolized and is excreted as unchanged drug in urine, dosage adjustment will not be necessary in patients with hepatic impairment Children: • Pregabalin is not licensed for use in children Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better

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• Because of an age-related reduction in renal function, lower pregabalin doses are appropriate and should be based on creatinine clearance values • Because pregabalin is associated with dizziness and somnolence the elderly are at increased risk of accidental injury (fall) • The elderly have an increased risk of loss of consciousness, confusion and mental impairment • Elderly cardiovascular compromised patients may have increased risk of congestive heart failure • Invariably the elderly are prescribed drug therapies for concurrent comorbidities, but the risk of pharmacokinetic interactions with pregabalin is low or nonexistent

Pregabalin

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Pregabalin is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than pregabalin monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • There are no available data on whether the pharmacokinetics of pregabalin change during pregnancy Breast feeding • Breast milk:  it is not known whether pregabalin is excreted in breast milk • Breastfed infants: it is not known what plasma pregabalin concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

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The overall place of pregabalin in the treatment of epilepsy Pregabalin appears to be a narrow-spectrum antiepileptic drug whose role in the management of partial seizures has yet to be fully

the epilepsy prescriber’s guide to antiepileptic drugs ascertained. Pregabalin should be used as adjunctive therapy in patients with intractable partial seizures who have failed to respond to other antiepileptic drug combinations.

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Primary seizure types: • Partial seizures Secondary seizure types: • None

Potential disadvantages: • Exaggerates myoclonus • Requires two–three times a day dosing • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Ben-Menachem E. Pregabalin pharmacology and its relevance to clinical practice. Epilepsia 2004; 45(Suppl 6): 13–18. Corrigan BW, Poole WF, Posvar EL, Strand JC, Alvey CW, Radulovic LL. Metabolic disposition of pregabalin in healthy volunteers. Clinical Pharmacology and Therapeutics 2001; 69: P18. Elger CE, Brodie MJ, Anhut H, Lee CM, Barrett JA. Pregabalin add-on treatment in patients with partial seizures: a novel evaluation of flexible-dose and fixed-dose treatment in a double-blind, placebo-controlled study. Epilepsia 2005; 46: 1926–1936. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Randnitis EJ, Posver EL, Alvey CW, Sedman AJ, Cook JA, Bockbrader HN. Pharmacokinetics of pregabalin in subjects with various degrees of renal function. Journal of Clinical Pharmacology 2003; 43: 277–283. Taylor CP, Angelotti T, Fauman E. Pharmacology and mechanism of action of pregabalin: the calcium channel α2-δ (alpha2 – delta) subunit as a target for antiepileptic drug discovery. Epilepsy Research 2007; 73: 137–150.

Pregabalin, overall role

Potential advantages: • Pregabalin is generally well-tolerated, with only mild adverse effects • More potent and probably better tolerated than gabapentin • Because it is excreted exclusively by renal elimination, pregabalin is not associated with any significant pharmacokinetic interactions • Drug absorption and clinical efficacy may be more consistent at high doses for pregabalin compared with gabapentin because of the higher potency of pregabalin and the fact that, unlike gabapentin, it is transported by more than one transport system

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Primidone Therapeutics Chemical name and structure: Primidone,   5 -ethyldihydro-5-phenyl-4,6(1-H,5H)pyrimidinedione, is a white crystalline substance, with a molecular weight of 218.25 and an empirical formula of C12H14N2O2 . O

H N N

O

H

Primidone

Brand names: • Apo-primidone • Cyral • Liskantin • Majsolin; Mizodin; Mutigan; Mylepsinum; Myidone; Mysoline • Primidon; Prysoline • Sertan Generics available: • Yes Licensed indications for epilepsy: • Monotherapy or adjunctive therapy in the control of grand mal, psychomotor and focal seizures in adults and children (FDA-PI) • For the management of grand mal and psychomotor (temporal lobe) epilepsy (UK-SPC) • For the management of focal and Jacksonian seizures, myoclonic jerks and akinetic attacks (UK-SPC) Licensed indications for non-epilepsy conditions: • Essential tremor (UK-SPC) Nonlicensed use for epilepsy: • Juvenile myoclonic epilepsy • Primarily generalized tonic–clonic seizures Nonlicensed use for non-epilepsy conditions: • There are none

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Ineffective (contraindicated): • Absence seizures

the epilepsy prescriber’s guide to antiepileptic drugs Mechanism of action: Because primidone is rapidly converted to phenobarbital, it is considered that phenobarbital is the primary contributor to the pharmacological effects of primidone • The mechanism of action of primidone itself has not been elucidated • Primidone exerts well-demonstrated seizure protection that is independent from phenobarbital • Mechanisms of action demonstrated for phenobarbital include: –– Enhancement of γ-aminobutyric acid (GABA) inhibition –– Enhances postsynaptic GABA A receptor-mediated chloride currents by prolonging the opening of the chloride-ionophore –– Concentration-dependent reduction of calcium-depen­dent action potentials

Pharmacokinetics Absorption and distribution: • Oral bioavailability: >90% • Food co-ingestion:  it is not known whether food co-ingestion affects either the speed or the extent of absorption • Tmax: 2–4 hours (adults); 4–6 hours (children) • Time to steady state: 2–4 days (primidone); 15–29 days (for derived phenobarbital) • Pharmacokinetics: linear • Protein binding: 10% • Volume of distribution: 0.5–0.8 L/kg

Pharmacokinetics

Efficacy profile: • The goal of treatment is complete remission of seizures • The full therapeutic effect of primidone may not be achieved until steady-state levels of phenobarbital are reached • Being converted to phenobarbital, primidone will have all of the efficacies of phenobarbital • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • Used mainly for partial seizures and generalized convulsive seizures • In contrast to phenobarbital, primidone is not used in neonates with seizure • Although phenobarbital has proven efficacy for the prophylactic treatment of febrile seizures, primidone is not used for this indication • Juvenile myoclonic epilepsy also responds to primidone, although it is no longer a drug of first choice because valproic acid and other antiepileptic drugs have become available • If primidone is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Primidone 222

• Salivary concentrations:  it is not known whether primidone is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma Metabolism: • Primidone is metabolized in the liver to two primary metabolites, namely phenobarbital and phenyl-ethyl-malonamide (PEMA) • Phenobarbital subsequently undergoes metabolism to two metabolites, p-hydroxyphenobarbital and 9-D-glucopyranosylpheno­ barbital • PEMA is pharmacologically active and can be measured in the plasma of patients taking primidone, but has a much lower potency than primidone and phenobarbital • At steady-state during chronic primidone therapy, plasma levels of primidone and phenobarbital are similar (phenobarbital: primidone ratio ~1.5), but during co-medication with an enzymeinducing drug, phenobarbital plasma levels may be three–five times higher than primidone levels • Phenobarbital undergoes autoinduction so that its clearance can increase and this may require an upward dosage adjustment of primidone when prescribed as monotherapy Elimination: • In the absence of enzyme-inducing AEDs, half-life values for primidone in adults are 7–22 hours • In the presence of enzyme-inducing co-medication, half-life values for primidone in adults are 3–12 hours • Half-life values in children are 5–11 hours • Half-life values in newborns are 8–80 hours • Renal excretion:  during monotherapy ~65% of an administered dose is excreted as unchanged primidone in urine; during poly­ therapy with enzyme-inducing AEDs only ~40% is excreted as unchanged primidone in urine

Drug interaction profile Pharmacokinetic drug interactions: Because phenobarbital is invariably present during long-term primidone treatment, all of the effects of phenobarbital on other drugs described previously for phenobarbital can be expected with primidone, and all of the interactions affecting phenobarbital will also affect the phenobarbital derived from primidone • Interactions between AEDs: effects on primidone and phenobarbital: –– See Phenobarbital section above –– Phenytoin and carbamazepine can accelerate the conversion of primidone to phenobarbital, which results in decreased primidone levels and increased phenobarbital levels

the epilepsy prescriber’s guide to antiepileptic drugs –– Acetazolamide decreases the gastrointestinal absorption of primidone • Interactions between AEDs: effects by primidone: –– See Phenobarbital section above • Interactions between AEDs and non-AED drugs: effects on primidone and phenobarbital: –– See Phenobarbital section above –– Isoniazid inhibits primidone biotransformation, resulting in high primidone levels relative to phenobarbital levels • Interactions between AEDs and non-AED drugs:  effects by primidone: –– See Phenobarbital section above

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Pharmacodynamic drug interactions: • To date, none have been reported

Adverse effects

Hormonal contraception: • Primidone enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking primidone

Adverse effects How drug causes adverse effects: • Mechanism by which primidone causes adverse effects has not been established and is presumed to be the same as the mechanism invoked for its efficacy • In most instances, it is not possible to separate the adverse effects caused by primidone from those caused by phenobarbital • Because of the conversion to and significant accumulation of phenobarbital, primidone treatment can be associated with all the adverse effects of phenobarbital • The acute initial toxicity clearly differentiates primidone and phenobarbital; even after a low initial dose of primidone, some patients experience transient adverse effects  – usually drowsiness, dizziness, ataxia, nausea, and vomiting – that are so debilitating that they may be reluctant to take another dose; because this acute toxic reaction occurs before phenobarbital or PEMA is detected in the blood, it is considered to be caused by primidone itself • Tolerance rapidly develops to the initial acute toxicity of primidone Common adverse effects: The adverse effects listed below are attributable to primidone, phenobarbital, or both:

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• Sedation and drowsiness • Hyperactivity and irritability (especially in children) • CNS-related adverse effects are usually dose-dependent and are reversible: dysarthria, ataxia, incoordination, and nystagmus • Depression • Cognitive impairment • Decreased bone mineral density Life-threatening or dangerous adverse effects: • Stevens-Johnson syndrome, erythema multiforme, toxic epidermal necrolysis (very rare) • Hypersensitivity reactions, may lead to hepatic failure

Primidone

Rare and not life-threatening adverse effects: • Movement disorders, such as dyskinesia, may be induced by phenobarbital • Seizure exacerbation or de novo seizures • Hematologic toxicity, mainly megaloblastic anemia • Exacerbation of acute intermittent porphyria • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with primidone/phenobarbital; can be prevented by administration of vitamin K to the mother before delivery • Connective tissue disorders associated with long-term phenobarbital therapy (unusual in children), such as Dupuytren contractures, plantar fibromatosis, heel and knuckle pads, frozen shoulder, Peyronie disease, and diffuse joint pain • Loss of libido and erectile dysfunction Weight change: • Not common What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Primidone must be started at a low dose to avoid the acute initial toxicity • Dosage reduction in cases of presumably dose-related adverse effects • Consider calcium and vitamin D supplements in cases of decreased bone mineral density

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Dosing and use Usual dosage range: • Adults and children > 8 years: 750–1500 mg/day (10–20 mg/kg/day) • Children 2–8 years: 10–20 mg/kg • Infants (< 2 years of age): 10–25 mg/kg/day • Newborns: 15–25 mg/kg/day

the epilepsy prescriber’s guide to antiepileptic drugs Available formulations: • Tablets: 50 mg, 250 mg • Suspension: 250 mg/5 mL

Dosing tips: • Given the relatively short half-life of primidone, the daily dose of primidone is usually divided into 2 or more doses • In neonates, infants and children, it is preferable to divide the daily dose into three divided doses

Dosing and use

How to dose: • For adults and children over 8 years of age: start treatment with 125 mg at night; the dose can then be increased every 3 days as tolerated, to a final daily maintenance dose of 10–20 mg/kg/day; some patients initially need as little as one-quarter tablet (62.5 mg) or a 50-mg tablet. Divide daily dose into two–three doses • Children and infants:  start treatment with 50 mg or less at night; the dose can then be increased every 3 days as tolerated, to a final maintenance dose of 10–25 mg/kg/day in infants, and 10–20 mg/ kg/day in children. Divide daily dose into two–three doses • Newborns:  15–25 mg/kg/day in divided doses two–four times/day; start with lower dosage and titrate upward; conversion of primidone to phenobarbital is slow in newborns, and phenobarbital levels are lower than primidone levels, even after 5 days of treatment

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How to withdraw drug: • May need to adjust dosage of concurrent medications as primidone is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • After long-term administration, primidone should always be discontinued gradually over several weeks • Barbiturates and benzodiazepines are the antiepileptic drugs most commonly associated with withdrawal seizures upon rapid discontinuation • Unless there is a specific reason to proceed faster, it is appropriate to taper the primidone dose linearly over 3–6 months, with reductions every 2–4 weeks Overdose: • Similar to phenobarbital (see Phenobarbital section), but primidone overdose can specifically cause crystalluria, with possible renal failure, especially at primidone plasma levels of 200 mg/L (920 μmol/L) or above • Can be fatal, mostly secondary to cardiorespiratory failure • Symptoms include: constricted pupils, nystagmus, ataxia, somnolence, stupor or coma, pulmonary edema, and respiratory failure • In individuals who have not been previously exposed to phenobarbital, plasma levels at or above 80 mg/L are considered lethal

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Primidone 226

• Higher plasma levels may be tolerated by patients on chronic phenobarbital therapy • Treatment consists mainly of cardiorespiratory support • Alkalinization with sodium bicarbonate, intravenous hydration and forced diuresis accelerate the elimination of phenobarbital through the kidneys • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes phenobarbital from blood and, therefore, serves as a useful procedure in cases of primidone overdose • It is not known whether hemodialysis removes primidone from blood and, therefore, could serve as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Monitoring of blood count and liver function tests usually not necessary • Consider vitamin D level and dual energy x-ray absorptiometry (DEXA) bone scan in patients at risk for osteopenia • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at phenobarbital plasma concentrations of 10–40 mg/L (43–172 μmol/L) –– Optimum seizure control in patients on monotherapy is most likely to occur at primidone plasma concentrations of 5–10 mg/L (23–46 μmol/L) –– The phenobarbital conversion factor from mg/L to μmol/L is 4.31 (i.e., 1 mg/L = 4.31 μmol/L) –– The primidone conversion factor from mg/L to μmol/L is 4.59 (1 mg/L = 4.59 mmol/L) –– Monitoring primidone levels is of little help in clinical practice; if blood levels are used to adjust the primidone dose, then phenobarbital rather than primidone levels are preferred because, at the usual concentration ratios, the adverse effects from a high phenobarbital level are more likely to limit further dosage increases –– The reference range of phenobarbital (and primidone) in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Phenobarbital can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant –– There are no data indicating the usefulness of monitoring primidone by use of saliva Do not use: • In patients with known history of allergic reaction to barbiturates • In patients with known history of intermittent acute porphyria • For the treatment of absence seizures

the epilepsy prescriber’s guide to antiepileptic drugs Special populations Renal impairment: • Primidone is renally excreted and phenobarbital is renally secreted, therefore, the dose of primidone may need to be lowered

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Hepatic impairment: • Primidone is substantially metabolized and phenobarbital is extensively metabolized in the liver and consequently lower doses of primidone may be required

Elderly: • Elderly patients are more susceptible to adverse effects of primidone and phenobarbital (especially somnolence) and, therefore, often do better at lower doses or even lower levels • Because of an age-related reduction in renal and hepatic function, lower primidone doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with primidone is substantial Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Primidone is classified by the US Food and Drug Administration as risk category D (positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy) • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Seizures, even mild seizures, may cause harm to the embryo/fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than primidone monotherapy • Taper drug if discontinuing • Vitamin K-deficient hemorrhagic disease in newborns of mothers treated with phenobarbital or primidone; can be prevented by administration of vitamin K to the mother before delivery

Special populations

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

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• During pregnancy primidone pharmacokinetics change significantly so that at late gestation primidone clearance increases by ~20%, whereas plasma concentrations of derived phenobarbital decrease by 50–70%, the latter due to increased clearance and reduction in albumin concentrations; an increase in primidone dose may be required in some patients

Primidone

Breast feeding • Breast milk: 40–96% (mean, 75%) of maternal plasma levels • Breast milk: phenobarbital: 30–50% of maternal plasma levels • Breastfed infants:  primidone can accumulate to levels that are similar to maternal plasma levels • Breastfed infants: phenobarbital plasma levels may reach 50->100% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects, including sedation, poor sucking and weight gain, and vomiting • If adverse effects are observed recommend bottle feed

The overall place of primidone in the treatment of epilepsy Primidone is currently a drug of second or third choice in patients with partial onset or generalized convulsive seizures. Because of its sedative and cognitive effects, it is never a drug of first choice. Its spectrum of use is more limited than that of phenobarbital, but it may at times be effective when other drugs have failed. Primary seizure types: • Partial and secondarily generalized seizures Secondary seizure types: • Juvenile myoclonic epilepsy • Primarily generalized tonic–clonic seizures Potential advantages: • Low systemic toxicity • Relatively inexpensive

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Potential disadvantages: • Primidone and phenobarbital produce more sedative and behavioral adverse effects than most other antiepileptic drugs • Associated with significant pharmacokinetic interactions and usually acts as an inducer of hepatic metabolism • Potential teratogen, but not more than most other antiepileptic drugs

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Primidone, overall role

Suggested reading Kuhnz W, Koch S, Helge H, Nau H. Primidone and phenobarbital during lactation period in epileptic women: total and free drug serum levels in the nursed infants and their effects on neonatal behavior. Developmental Pharmacology and Therapeutics 1988; 11: 147–154. Leppik IE, Cloyd JC, Miller K. Development of tolerance to the side effects of primidone. Therapeutic Drug Monitoring 1984; 6: 189–191. Mattson RH, Cramer JA, Collins JF, Smith DB, Delgado-Escueta AV, Browne TR, Williamson PD, Treiman DM, McNamara JO, McCutchen CB. Comparison of carbamazepine, phenobarbital, phenytoin, and primidone in partial and secondarily generalized tonic-clonic seizures. New England Journal of Medicine 1985; 313: 145–151. Nau H, Rating D, Hauser I, Jäger E, Koch S, Helge H. Placental transfer and pharmacokinetics of primidone and its metabolites phenobarbital, PEMA and hydroxyphenobarbital in neonates and infants of epileptic mothers. European Journal of Clinical Pharmacology 1980; 18: 31–42. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Sapin JI, Riviello JJ, Grover WD. Efficacy of primidone for seizure control in neonates and young infants. Pediatric Neurology 1988; 4: 292–295. van Heijst AN, de Jong W, Seldenrijk R, van Dijk A. Coma and crystalluria:  a massive primidone intoxication treated with haemoperfusion. Journal of Toxicology and Clinical Toxicology 1983; 20: 307–318.

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Rufinamide Therapeutics Chemical name and structure: Ruf inam ide,   1-[(2,6 -dif luorophenyl)methyl]-1-hydro-1,23 triazole-4carboxamide, is a white powder, with a molecular weight of 238.19 and an empirical formula of C10H8F2N4O. F N N

N

F

NH2

Rufinamide

O Brand names: • Banzel • Inovelon Generics available: • No Licensed indications for epilepsy: • Adjunctive treatment of seizures in Lennox-Gastaut syndrome in patients 4 years and older (UK-SPC; FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Data on seizure contraindications are not available

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Mechanism of action: • Acts as a blocker of voltage-sensitive sodium channels • Prevents sodium channels from returning to an activated state (from an inactivated state) thereby preventing the generation of sustained bursts of high frequency action potentials

the epilepsy prescriber’s guide to antiepileptic drugs Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 4 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If rufinamide is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Pharmacokinetics

Pharmacokinetics Absorption and distribution: • Oral bioavailability: not determined, however, it is dose-­dependent in that as dose increases the bioavailability decreases • Food co-ingestion: substantially [mean, 44%] increases the amount of rufinamide absorbed, Cmax values are increased by ~100%, whereas Tmax values are shortened (6 hours vs. 8 hours when fasted) • Tmax: 4–6 hours • Time to steady state: 1–2 days • Pharmacokinetics:  linear up to 1600 mg/day; nonlinear >1600 mg/day due to reduced oral bioavailability • Protein binding: 35% • Volume of distribution: 0.71–1.14 L/kg • Salivary concentrations:  it is not known whether rufinamide is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

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Metabolism: • Rufinamide is metabolized in the liver, primarily by hydrolysis which is not CYP-dependent, to CGP 47292 • CGP 47292 is excreted in urine (~70%) and feces (~9%) • Approximately 7% is excreted in urine as minor acyl-glucuronide metabolites of CGP 47292 • The metabolites of rufinamide are not pharmacologically active • Autoinduction is not a feature of rufinamide metabolism Elimination: • The plasma half-life in healthy volunteers and in patients with epilepsy is 6–10 hours • Clearance values in children can be expected to be ~50% greater • Clearance values in females are lower than for males • Renal excretion: ~4% of an administered dose is excreted unchanged in urine

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Rufinamide

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on rufinamide: –– Carbamazepine, phenobarbital, phenytoin, primidone, and vigabatrin can increase the clearance of rufinamide and decrease rufinamide plasma levels –– Valproic acid can decrease the clearance of rufinamide and increase rufinamide plasma levels • Interactions between AEDs: effects by rufinamide: –– Rufinamide can decrease plasma levels of carbamazepine and lamotrigine –– Rufinamide can increase plasma levels of phenobarbital and phenytoin • Interactions between AEDs and non-AED drugs:  effects on rufinamide: –– To date, there have been no reports of other non-AED drugs affecting the clearance of rufinamide and affecting rufinamide plasma levels • Interactions between AEDs and non-AED drugs:  effects by rufinamide: –– Rufinamide can decrease plasma levels of triazolam Pharmacodynamic drug interactions: • To date, none have been reported Hormonal contraception: • Rufinamide enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking rufinamide

Adverse effects How drug causes adverse effects: • Not known Common adverse effects: • Dizziness, diplopia, somnolence • Nausea, vomiting, fatigue

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Life-threatening or dangerous adverse effects: • Hypersensitivity syndrome (fever, rash, lymphadenopathy, liver function test abnormalities and hematuria) • Decreases QTc interval, therefore, patients with congenital short QT syndrome or a family history of the syndrome may be at risk • Increased frequency of status epilepticus

the epilepsy prescriber’s guide to antiepileptic drugs Rare and not life-threatening adverse effects: • To date there are none

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Weight change: • Not common

Dosing and use Usual dosage range: • Weight range <30 kg: up to a maximum dose of 1000 mg/day • Weight range 30–50 kg: up to a maximum dose of 1800 mg/day • Weight range 50.1–70 kg: up to a maximum dose of 2400 mg/day • Weight range >70 kg: up to a maximum dose of 3200 mg/day

Dosing and use

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • CNS-related adverse effects are usually dose-dependent, are reversible and are prevented by slow and upward titration following ­initiation of treatment • Risk of serious adverse effects is greatest in the first few months of treatment • Common adverse effects such as sedation often abate after a few months

Available formulations: • Tablets: 100 mg, 200 mg, 400 mg How to dose: • When initiating rufinamide treatment start with a low dose and titrate slowly so as to minimize adverse effects. –– For children 4 years of age or older and less than 30 kg and not receiving valproic acid: start treatment with 100 mg twice daily; every 2 days increase by 200 mg/day in divided doses; maintenance dose generally 1000 mg/day –– For children 4 years of age or older and less than 30 kg and receiving valproic acid: start treatment with 100 mg twice daily; every 2 days increase by 200 mg/day in divided doses; maintenance dose generally 400–600 mg/day –– For adults and children 4 years or older of 30 kg or over:  start treatment with 200 mg twice daily; every 2 days increase by 400 mg/ day in divided doses; maintenance dose generally 1800 mg/day (30–50 kg), 2400 mg/day (50.1–70 kg), and 3200 mg/day (>70 kg) Dosing tips: • Should be ingested twice daily with water in the morning and in the evening, in two equally divided doses.

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• As food enhances the absorption of rufinamide, it is preferable to ingest rufinamide with food • If patient has difficulty swallowing, tablets can be crushed and administered in half a glass of water How to withdraw drug: • May need to adjust dosage of concurrent medications as rufinamide is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper: reduce dose by ~25% every 2 days • Rapid discontinuation may increase the risk of seizures

Rufinamide

Overdose: • To date, no cases have been reported • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes 30% of rufinamide from blood and, therefore, may be a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Before starting: liver and kidney function tests • Consider ECG to rule out short QT syndrome • During treatment: liver and kidney function tests every 12 months • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at rufinamide plasma concentrations of 10–25 mg/L (42–105 μmol/L) –– The conversion factor from mg/L to μmol/L is 4.20 (i.e., 1 mg/L = 4.20 μmol/L) –– The reference range of rufinamide in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– There are no data indicating the usefulness of monitoring rufinamide by use of saliva Other warnings/precautions: • To date there are none

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Do not use: • If patient has congenital short QT syndrome or a family history of the syndrome • If patient has a proven allergy to rufinamide or to any of the excipients which include lactose • Because formulation contains lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency, or glucose–galactose malabsorption should not take this medicine

the epilepsy prescriber’s guide to antiepileptic drugs Special populations Renal impairment: • Rufinamide is renally secreted and thus the dose may need to be lowered in renally impaired patients • Because rufinamide can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of rufinamide

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Hepatic impairment: • Rufinamide is extensively metabolized in the liver and consequently lower doses may be required

Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in hepatic function, lower rufinamide doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with rufinamide is moderate Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Rufinamide is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than rufinamide monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of rufinamide during pregnancy are not available

Special populations

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

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Breast feeding • Breast milk:  it is not known whether rufinamide is excreted in breast milk • Breastfed infants: it is not known what plasma rufinamide concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (e.g., sedation) • If adverse effects are observed recommend bottle feed

Rufinamide

The overall place of rufinamide in the treatment of epilepsy Rufinamide is licensed by the European Medicines Agency as an Orphan Drug for use specifically as adjunctive treatment of seizures associated with Lennox-Gastaut syndrome in patients aged 4 years and older. Consequently it is too early to ascertain the place of rufinamide in the treatment of patients with epilepsy. Primary seizure types: • Seizures associated with Lennox-Gastaut syndrome (absences, myoclonic, tonic, and atonic [drop attacks]) Secondary seizure types: • None Potential advantages: • Rufinamide is effective in Lennox-Gastaut syndrome, a difficult to treat syndromic epilepsy Potential disadvantages: • Nonlinear bioavailability • Need to co-ingest food so as to optimize bioavailability • Associated with pharmacokinetic interactions • Potential teratogen, but not more than most other antiepileptic drugs

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Suggested reading Arroyo S. Rufinamide. Neurotherapeutics 2007; 4: 155–162. Cardot JM, Lecaillon JB, Czendlik C, Godbillon J. The influence of food on the disposition of the antiepileptic rufinamide in healthy volunteers. Biopharmacy and Drug Disposition 1998; 19: 259–262. Deeks ED, Scott LJ. Rufinamide. CNS Drugs 2006; 20: 751–761. Glauser T, Kluger G, Sachdeo R, Krauss G, Perdomo C, Arroyo S. Rufinamide for generalized seizures associated with LennoxGastaut syndrome. Neurology 2008; 70: 1950–1958.

the epilepsy prescriber’s guide to antiepileptic drugs McLean MJ, Schmutz M, Pozza MF, Wamil A. The influence of rufinamide on sodium currents and action potential firing in rodent neurons. Epilepsia 2005; 46(Suppl 6): 375. Perucca E, Cloyd J, Critchley D, Fuseau E. Rufinamide:  clinical pharmacokinetics and concentration-response relationships in patients with epilepsy. Epilepsia 2008; 49: 1123–1141.

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Stiripentol Therapeutics Chemical name and structure: Stiripentol, 4,4-dimethyl-1[3,4(methylenedioxy)-phenyl]-1-pentan3-ol, is a pale pink crystalline powder, with a molecular weight of 234 and an empirical formula of C14H18O3. OH O

O

Stiripentol

Brand names: • Diacomit Generics available: • No Licensed indications for epilepsy: • Adjunctive treatment of seizures in children with severe myoclonic epilepsy in infancy (Dravet syndrome) • Has been authorized under a “conditional approval” scheme by the European Medicines Agency (i.e., further evidence on stiripentol is awaited, in particular about its efficacy in combination with the maximum safe dose of the add-on therapy) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • Adjunctive treatment with carbamazepine in children with refractory partial seizures Nonlicensed use for non-epilepsy conditions: • There are none Ineffective (contraindicated): • Carbamazepine, phenytoin and phenobarbital should not be used in conjunction with stiripentol in the management of Dravet syndrome

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Mechanism of action: • Increases brain GABA levels by inhibition of synaptic uptake of GABA and/or inhibition of GABA-transaminase

the epilepsy prescriber’s guide to antiepileptic drugs • Enhances GABA A receptor-mediated transmission and increases the mean-duration (but not the frequency) of GABA A receptor chloride channels by a barbiturate-like mechanism • Most of the actions of stiripentol during adjunctive treatment are probably indirect and mediated by inhibition of cytochrome P450 enzymes and increasing concurrent antiepileptic drug blood levels

Pharmacokinetics Absorption and distribution: • Oral bioavailability: not determined • Food co-ingestion: food co-ingestion is essential because stiripentol degrades rapidly in the acidic environment of an empty stomach • Tmax: 1.5 hours • Time to steady state: <7 days • Pharmacokinetics: nonlinear (due to saturable metabolism) so that clearance decreases with increasing dose • Protein binding: 99% • Volume of distribution: not known • Salivary concentrations:  it is not known whether stiripentol is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

Pharmacokinetics

Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 2–4 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If stiripentol is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

S

Metabolism: • Stiripentol is metabolized in the liver, primarily by desmethylation and glucuronidation, to 13 different metabolites • Precise identification of enzymes involved in metabolism not known but the principal enzymes are considered to be CYP1A2, CYP2C19, and CYP3A4 • The metabolites of stiripentol are not considered to be pharmacologically active • Autoinduction is not a feature of stiripentol metabolism Elimination: • Plasma half-life and clearance is dose-dependent with values decreasing with increasing dose • Renal excretion: ~73% of an administered dose is excreted in urine as metabolites

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Stiripentol

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on stiripentol: –– Carbamazepine, phenobarbital, phenytoin, and primidone can increase the clearance of stiripentol and decrease stiripentol plasma levels • Interactions between AEDs: effects by stiripentol: –– Stiripentol can increase plasma levels of carbamazepine, phenobarbital, valproic acid, and clobazam and its pharmacologically active metabolite N-desmethylclobazam • Interactions between AEDs and non-AED drugs:  effects on stiripentol: –– To date, there have been no reports of other non-AED drugs affecting the clearance of stiripentol and affecting stiripentol plasma levels • Interactions between AEDs and non-AED drugs:  effects by stiripentol: –– To date, there have been no reports of stiripentol affecting the clearance of other non-AED drugs and affecting their plasma levels –– However, because stiripentol is a potent inhibitor of CYP2C19, CYP3A4, and CYP2D6, caution needs to be exercised if clinical circumstances require combining stiripentol with drugs that are metabolized by these isoenzymes (e.g., citalopram, omeprazole [CYP2C19]; astemizole, chlorpheniramine, calcium channel blockers, statins, codeine [CYP3A4]; propranolol, fluoxetine, sertraline, haloperidol, tramadol [CYP2D6] Pharmacodynamic drug interactions: • Enhances anorexia and loss of appetite associated with valproic acid • In the absence of available clinical data, caution should be taken when stiripentol is co-administered with the following drugs: –– Cisapride, halofantrine, pimozide, quinidine, bepridil: increased risk of cardiac arrhythmias and torsades de pointes/wave burst arrhythmias in particular –– Chlorpromazine: enhances its central depressant effects Hormonal contraception: • It is not known whether stiripentol affects hormonal contraception but theoretically it can increase plasma levels of hormonal contraceptives and thus necessitate lower doses to be prescribed

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Adverse effects How drug causes adverse effects: • Not known

the epilepsy prescriber’s guide to antiepileptic drugs Common adverse effects: • Anorexia, loss of appetite, nausea, vomiting • Drowsiness, ataxia, hypotonia and dystonia, hyperkinesias • Insomnia, aggressiveness, irritability, behavior disorders, hyper­ excitability

S

Life-threatening or dangerous adverse effects: • Cutaneous photosensitivity, rash, and urticaria Rare and not life-threatening adverse effects: • To date there are none Weight change: • Weight gain is common (especially when co-administered with valproic acid)

Dosing and use

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Risk of serious adverse effects is greatest in the first few months of treatment • Many of the adverse effects associated with stiripentol are often due to an increase in plasma levels of concomitant antiepileptic drugs and usually regress when the dose of these antiepileptic drugs is reduced Dosing and use Usual dosage range: • Initially 50 mg/kg/day (in combination with clobazam and valproic acid) but up to a maximum of 4 g. Available formulations: • Capsules: 250 mg, 500 mg • Sachets: 250 mg, 500 mg How to dose: When initiating stiripentol treatment start with a low dose and titrate slowly so as to minimize adverse effects • The initial dose should be 50 mg/kg/day administered either twice daily or thrice daily; every 3 days increase by 100 mg/kg/day in divided doses to a maximum dose of 4 g • It should be noted that the pivotal clinical evaluation of stiripentol was in children of 3 years of age and over with Dravet syndrome. The clinical decision for use of stiripentol in children < 3 years of age needs to be made on an individual patient basis taking into consideration the potential clinical benefit and risks

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Dosing tips: • Bioequivalence between the capsule and oral suspension (sachet) formulations has not been determined and, therefore, clinical supervision is recommended if changing stiripentol formulation • Should be ingested twice or thrice daily with water • Because of the inhibitory interactions with clobazam and valproic acid, daily dosage of these antiepileptic drugs may need to be reduced by 25–30% • Because acid exposure, as occurs with gastric acid on an empty stomach, rapidly degrades stiripentol, it must always be ingested with food • If patient has difficulty swallowing, the sachet powder formulation can be mixed in a glass of water and ingested immediately after mixing • Stiripentol should not be ingested with milk, dairy products (yogurt, soft cream cheeses, etc.), or carbonated drinks

Stiripentol

How to withdraw drug: • May need to adjust dosage of concurrent medications as stiripentol is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper: reduce dose by 50 mg/kg/day every 3 days • Rapid discontinuation may increase the risk of seizures Overdose: • To date, no cases have been reported • If indicated the stomach should be emptied by lavage or by induction of emesis • It is not known whether hemodialysis removes stiripentol from blood and, therefore, serves as a useful procedure in cases of overdose

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Tests and therapeutic drug monitoring: • Before starting: blood count and liver and renal function tests • During treatment: blood count and liver and renal function tests every 12 months • Therapeutic drug monitoring: –– Stiripentol plasma concentrations associated with optimum seizure control in patients prescribed stiripentol have not been identified –– Monitoring of concomitant antiepileptic drugs is essential because stiripentol inhibits the metabolism of many antiepileptic drugs –– There are no data indicating the usefulness of monitoring stiri­ pentol by use of saliva • Before giving a drug that can cause weight gain to an overweight or obese patient, consider determining whether the patient already has prediabetes (fasting plasma glucose 100–125 mg/dL), diabetes (fasting plasma glucose greater than 126 mg/dL), or dyslipidemia (increased total cholesterol, LDL cholesterol and triglycerides; decreased HDL

the epilepsy prescriber’s guide to antiepileptic drugs cholesterol), and treat or refer such patients for treatment, including nutrition and weight management, physical activity counseling, smoking cessation, and medical management • Monitor weight and BMI during treatment

Do not use: • If patient is hypersensitive to the stiripentol or its excipients • If a patient has a history of psychoses in the form of episodes of delirium

special populations

Other warnings/precautions: • Given the frequency of gastrointestinal adverse reactions to treatment with stiripentol and valproic acid (anorexia, loss of appetite, nausea, vomiting), children co-administered these antiepileptic drugs should have their growth rate carefully monitored • Because stiripentol is a potent inhibitor of hepatic enzymes, the following drug combinations require particular caution: –– Rye ergot alkaloids (ergotamine, dihydroergotamine): ergotism with possibility of necrosis of the extremities –– Immunosuppressants (tacrolimus, cyclosporine, sirolimus): neph­rotoxicity –– Statins (atorvastatin, simvastatin, etc.): rhabdomyolysis –– Theophylline, caffeine: toxicity

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Special populations Renal impairment: • In the absence of specific clinical data in patients with impaired renal function, stiripentol should not be prescribed to such patients Hepatic impairment: • In the absence of specific clinical data in patients with impaired hepatic function, stiripentol should not be prescribed to such patients • However, because stiripentol is extensively metabolized in the liver, lower doses would be required Children: • Stiripentol is licensed for exclusive use in children • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults Elderly: • Stiripentol should not be prescribed to elderly patients Pregnancy: • In view of the indication for stiripentol, its administration during pregnancy and in women of childbearing potential would not be expected; however, if it occurs specialist advice should be given to

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Stiripentol

women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Stiripentol is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other AEDs in combination may cause a higher prevalence of teratogenic effects than stiripentol monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of stiripentol during pregnancy are not available Breast feeding • Breast milk:  it is not known whether stiripentol is excreted in breast milk • Breastfed infants: it is not known what plasma stiripentol concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (e.g., sedation) • If adverse effects are observed recommend bottle feed

The overall place of stiripentol in the treatment of epilepsy Stiripentol is licensed for use as adjunctive treatment of seizures associated with Dravet syndrome in patients aged 3 years and older. It is unlikely that stiripentol will be licensed for adult patients with other types of epilepsy and, therefore, stiripentol is not expected to have a significant role in epilepsy management. Primary seizure types: • Seizures associated with Dravet syndrome (clonic and tonic–clonic attacks) Secondary seizure types: • None

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Potential advantages: • Effective in Dravet syndrome: a difficult to treat syndromic epilepsy

the epilepsy prescriber’s guide to antiepileptic drugs Potential disadvantages: • Associated with nonlinear pharmacokinetics so that plasma levels increase disproportionately to dose • Need to co-ingest food so as to optimize bioavailability • Associated with pharmacokinetic interactions and usually acts as an inhibitor of hepatic metabolism • Potential teratogen, but not more than most other antiepileptic drugs

Stiripentol, overall role

Suggested reading Cazali N, Tran A, Treluyer JM, Rey E, d’Athis P, Vincent J, Pons G. Inhibitory effect of stiripentol on carbamazepine and saquinavir metabolism in human. British Journal of Clinical Pharmacology 2003; 56: 526–536. Chiron C. Stiripentol. Neurotherapeutics 2007; 4: 123–125. Chiron C, Marchand MC, Tran A, d’Athis P, Vincent J, Dulac O, Pons G. Stiripentol in severe myoclonic epilepsy in infancy: a randomised placebo-controlled syndrome-dedicated trial. STICLO study group. Lancet 2000; 356: 1638–1642. Chiron C, Tonnelier S, Rey E, Brunet ML, Tran A, d’Athis P, Vincent J, Dulac O, Pons G. Stiripentol in childhood partial epilepsy: randomized placebo-controlled trial with enrichment and withdrawal design. Journal of Child Neurology 2006; 21: 496–502. Giraud C, Treluyer JM, Rey E, Chiron C, Vincent J, Pons G, Tran A. In vitro and in vivo inhibitory effect of stiripentol on clobazam metabolism. Drug Metabolism and Disposition 2006; 34: 608–611. Kassai B, Chiron C, Augier S, Cucherat M, Rey E, Gueyffier F, Guerrini R, Vincent J, Dulac O, Pons G. Severe myoclonic epilepsy in infancy:  a systematic review and meta-analysis of individual patient data. Epilepsia 2008; 49: 343–348.

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Sulthiame Therapeutics Chemical name and structure: Sulthiame, 4(1,1-diozothiazinan-2-yl)benzenesulfonamide, is a white powder, with a molecular weight of 290.04 and an empirical formula of C10H14N2O4S2. SO2NH2

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Brand names: • Ospolot Generics available: • No Licensed indications for epilepsy: • Treatment of rolandic epilepsy when treatment with other anti­ epileptic drugs has failed (licensed in Argentina, Austria, Czech Republic, Germany, Hungary, Israel, Slovakia, and Switzerland) Licensed indications for non-epilepsy conditions: • Behavioral disorders associated with epilepsy, hyperkinetic behavior, temporal lobe epilepsy, myoclonic seizures, generalized tonic– clonic seizures, Jacksonian seizures (licensed in Australia) Nonlicensed use for epilepsy: • Partial seizures with or without secondary generalization • Benign childhood epilepsies and epileptic encephalopathies, particularly those with EEG continuous spike-wave during sleep (e.g., pseudo-Lennox syndrome, bioelectric status epilepticus in nonREM sleep [ESES], Landau-Kleffner syndrome) • Infantile spasms (West syndrome)

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Nonlicensed use for non-epilepsy conditions: • There are none

the epilepsy prescriber’s guide to antiepileptic drugs Ineffective (contraindicated): • Data on seizure contraindications are not available

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Mechanism of action: • Inhibits voltage-gated sodium channels • Inhibits release of glutamate • Inhibits the enzyme carbonic anhydrase in glial cells which increases carbon dioxide concentrations leading to acidification of the extracellular space; this results in a reduction in inward currents associated with NMDA calcium receptors and causes depression of intrinsic neuronal excitability

Pharmacokinetics Absorption and distribution: • Oral bioavailability: 100% • Food co-ingestion: it is not known whether food co-ingestion affects absorption • Tmax: 1–5 hours • Time to steady state: ~3 days (adults); ~2 days (children) • Pharmacokinetics: linear • Protein binding: 29% • Volume of distribution: not determined • Salivary concentrations:  it is not known whether sulthiame is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma

Pharmacokinetics

Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 2 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If sulthiame is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Metabolism: • Sulthiame undergoes moderate metabolism in the liver by means of unknown isoenzymes to unknown metabolites • The metabolites of sulthiame are not considered to be pharmacologically active • Autoinduction is not a feature of sulthiame metabolism Elimination: • Half-life values in adults are 8–15 hours • Half-life values in children are 5–7 hours • Renal excretion: 80–90% of an administered dose is excreted in urine, of which 32% is as unchanged sulthiame

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Sulthiame

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on sulthiame: –– Carbamazepine and primidone can increase the clearance of sulthiame and decrease sulthiame plasma levels • Interactions between AEDs: effects by sulthiame: –– Sulthiame can increase plasma levels of lamotrigine, phenobarbital, and phenytoin • Interactions between AEDs and non-AED drugs:  effects on sulthiame: –– To date, there have been no reports of other non-AED drugs affecting the clearance of sulthiame and affecting sulthiame plasma levels –– Antacids containing magnesium trisilicate, bismuth oxycarbonate, and magnesium oxide may reduce sulthiame gastrointestinal absorption and decrease plasma sulthiame levels • Interactions between AEDs and non-AED drugs:  effects by sulthiame: –– To date, there have been no reports of sulthiame affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • Concomitant administration with primidone, particularly in children, is associated with a profound pharmacodynamic interaction whereby the intensity of undesirable adverse effects such as dizziness, uncertain gait, and drowsiness may be exacerbated • Because sulthiame is a sulphonamide derivative, concomitant administration with alcohol will result in similar adverse pharmacodynamic interactions to that observed with disulfiram and secondary to vasodilatation namely: pulsating headache, nausea, vomiting, respiratory depression, tachycardia, hypotension, amblyopia, arrhythmias, excitation, impairment of consciousness • Concomitant administration with other antiepileptic drugs (e.g., acetazolamide, topiramate, zonisamide) that inhibit carbonic anhydrase could potentially increase kidney stone formation, metabolic acidosis, hemodilution, and blood electrolyte changes Hormonal contraception: • It is not known whether or not sulthiame affects the metabolism of oral contraceptives but theoretically it can increase plasma levels of hormonal contraceptives and thus necessitate lower doses to be prescribed

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Adverse effects How drug causes adverse effects: • CNS adverse effects theoretically due to actions secondary to inhibition of carbonic anhydrase activity

the epilepsy prescriber’s guide to antiepileptic drugs Common adverse effects: • Paresthesias of the extremities and face • Tachypnea, hyperpnea, dyspnea • Dizziness, headache, diplopia • Stenocardia, tachycardia • Loss of appetite

Rare and not life-threatening adverse effects: • Anxiety • Hallucinations • Joint pain • Myesthetic phenomena

dosing and use

Life-threatening or dangerous adverse effects: • Rare induction of renal failure • Rare serious rash including Stevens-Johnson syndrome and toxic epidermal necrolysis (Lyell syndrome) or polyneuritis • As a carbonic anhydrase inhibitor, sulthiame is associated with adverse effects associated with such inhibition and include nephrolithiasis, metabolic acidosis, and hemodilution with changed electrolytes • In a single case sulthiame administration was associated with progressive weakness of the limbs, hypersalivation, slurred speech, and increasing drowsiness ending up in a coma • Increased seizure activity

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Weight change: • Weight loss can occur What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Many of the adverse effects are dose-dependent and will subside and disappear with dose reduction • Patients and their carers must be informed that if fever, sore throat, allergic skin reactions with swelling of lymph nodes, or flu-like symptoms occur, they should contact their physician immediately • It is advisable to perform regular checks of blood count and renal function so that if the above clinical symptoms are accompanied by thrombocytopenia or leukopenia, sulthiame should be discontinued • Sulthiame should be discontinued immediately if a severe allergic reaction occurs or if creatinine levels show a constant increase

Dosing and use Usual dosage range: • Adults: 200–600 mg/day • Children (2–12 years of age): 5–10 mg/kg/day

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Available formulations: • Tablets: 50 mg, 200 mg How to dose: • When initiating sulthiame treatment start with a low dose and titrate slowly so as to minimize adverse effects –– For adults:  start treatment with 50 mg twice daily; each week increase by 100 mg/day in divided doses until an optimum response is achieved; maintenance dose generally 200–600 mg/ day given in two equally divided doses –– Children:  start treatment with 5 mg/kg per day; each week increase by 5 mg/kg per day until an optimum response is achieved; maintenance dose generally 5–10 mg/kg/day given in two equally divided doses

Sulthiame

Dosing tips: • Slow dose titration may reduce the incidence of adverse effects • Tablets should only be administered as whole tablets with plenty of water; dose should be rounded down to the nearest whole tablet • If therapy is not successful within 1–2 months, sulthiame should be discontinued How to withdraw drug: • May need to adjust dosage of concurrent medications as sulthiame is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Taper: a gradual dose reduction over a period of 2 weeks should be undertaken • Rapid discontinuation may induce withdrawal seizures and should only be undertaken if there are safety concerns (e.g., a rash) Overdose: • Doses of 4–5 g have been associated with headache, dizziness, ataxia, impairment of consciousness, metabolic acidosis, and crystals in urine • A dose of 20 g resulted in a fatality in one case and in another case the patient survived with full recovery • Sodium bicarbonate may be administered as an infusion to treat the acidosis • If indicated the stomach should be emptied by lavage or by induction of emesis • It is not known whether hemodialysis removes sulthiame from blood and, therefore, serves as a useful procedure in cases of overdose

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Tests and therapeutic drug monitoring: • Before starting: blood count and kidney function test • During treatment: blood count and kidney function test at weekly intervals for the first month of treatment and thereafter at monthly

the epilepsy prescriber’s guide to antiepileptic drugs

Other warnings/precautions: • In some children seizure suppression and reduction in spike frequency by sulthiame may be associated with concurrent deterioration in cognitive function (e.g., memory decline, reduction in attention skill and mathematics ability) Do not use: • If patient has a proven allergy to sulthiame or other sulphonamides or to any of the excipients, which include lactose monohydrate • Because formulation contains lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency, or glucose–galactose malabsorption should not take this medicine • In patients with acute porphyria, hyperthyroidism, arterial hypertension, or a history of psychiatric disease

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Special populations

intervals; after 6 months of treatment these checks should be undertaken at 3- to 6-month intervals • Therapeutic drug monitoring: –– Optimum seizure control in adult patients on polytherapy is most likely to occur at plasma sulthiame concentrations of 2–10 mg/L (7–34 μmol/L) –– Optimum seizure control in children on polytherapy is most likely to occur at sulthiame plasma concentrations of 1–3 mg/L (3–10 μmol/L) –– The conversion factor from mg/L to μmol/L is 3.45 (i.e., 1 mg/L = 3.45 μmol/L) –– There are no data indicating the usefulness of monitoring sul­ thiame by use of saliva

Special populations Renal impairment: • Sulthiame is renally excreted and the dose may need to be lowered in renally impaired patients • Because it is not known whether sulthiame can be removed by hemodialysis, it is not known whether patients receiving hemodialysis require supplemental doses of sulthiame Hepatic impairment: • Sulthiame undergoes moderate metabolism in the liver and consequently lower doses will be required in patients with hepatic impairment Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults

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Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in hepatic function, lower sulthiame doses are appropriate • Because sulthiame is associated with impaired alertness and reaction capacity, the elderly may have reduced ability to drive a car, operate machinery or perform other activities requiring increased alertness • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with sulthiame is substantial

Sulthiame

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Sulthiame is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than sulthiame monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • It is unknown whether the pharmacokinetics of sulthiame changes during pregnancy Breast feeding • Breast milk:  it is not known whether sulthiame is excreted in breast milk • Breastfed infants: it is not known what plasma sulthiame concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

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The overall place of sulthiame in the treatment of epilepsy The good tolerability, significant efficacy and convenience of use suggest that sulthiame should become a first-line drug in the treatment of benign partial epilepsies of childhood and juvenile

the epilepsy prescriber’s guide to antiepileptic drugs myoclonic epilepsy. There appears to be no significant difference between carbamazepine and sulthiame in the treatment of benign childhood epilepsy with centrotemporal spikes. It also has a role as add-on treatment in other partial and myoclonic epilepsies. With regard to seizures secondary to Rett syndrome, sulthiame may be a good alternative to carbamazepine, particularly in those patients where carbamazepine is not effective or not well tolerated. Sulthiame has comparable efficacy to vigabatrin in the management of West syndrome.

Secondary seizure types: • None Potential advantages: • Particularly useful in various childhood epilepsies • Not associated with significant adverse effects

Sulthiame, overall role

Primary seizure types: • Benign childhood epilepsies:  rolandic epilepsy, pseudo-Lennox syndrome, Landau-Kleffner syndrome • Epileptic encephalopathies, particularly those with EEG continuous spike-wave during sleep

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Potential disadvantages: • Associated with significant pharmacokinetic interactions, particularly with phenytoin, and usually acts as an inhibitor of hepatic metabolism • Has limited licensed indications in only a few countries world-wide • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Debus OM, Kurlemann G; Study group. Sulthiame in the primary therapy of West syndrome:  a randomized double-blind placebocontrolled add-on trial on baseline pyridoxine medication. Epilepsia 2004; 45: 103–108. Doose H, Baier WK, Ernst JP, Tuxhorn I, Volzke E. Benign partial epilepsy – treatment with sulthiame. Developmental Medicine and Child Neurology 1988; 30: 683–684. Freilinger M, Seidl R, Hauser E. Carbamazepine, oxcarbazepine and sulthiame in newly diagnosed benign epilepsy of childhood with rolandic spikes. Epilepsia 1997; 38(Suppl 3): 97–98. Hansen JM, Kristensen M, Skovsted L. Sulthiame (Ospolot), an inhibitor of diphenylhydantoin metabolism. Epilepsia 1968; 9: 17–22. Houghton GW, Richens A. Inhibition of phenytoin metabolism by sulthiame. British Journal of Pharmacology 1973; 49: 157–158.

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Huppke P, Kohler K, Brockmann K, Stettner GM, Gartner J. Treatment of epilepsy in Rett syndrome. European Journal of Paediatric Neurology 2007; 11: 10–16. Koepp MJ, Patsalos PN, Sander JWAS. Sulthiame in adults with refractory epilepsy and learning disability: an open trial. Epilepsy Research 2002; 50: 277–282. Kramer U, Shahar E, Zelnik N, Lerman-Sagie T, Watemberg N, Nevo Y, Ben-Zeev B. Carbamazepine versus sulthiame in treating benign childhood epilepsy with centrotemporal spikes. Journal of Child Neurology 2002; 17: 914–916. Lerman P, Nussbaum E. The use of sulthiame in myoclonic epilepsy of childhood and adolescence. Acta Neurologica Scandinavica 1975: 60(Suppl): 7–12. May TW, Korn-Merker E, Rambeck B, Boenigk HE. Pharmaco­ kinetics of sulthiame in epileptic patients. Therapeutic Drug Monitoring 1994; 16: 251–257. Rating D, Wolf C, Bast T. Sulthiame as monotherapy in children with benign childhood epilepsy with centrotemporal spikes:  a 6-month randomized, double-blind, placebo-controlled study. Sulthiame Study Group. Epilepsia 2000; 41: 1284–1288. Wirrell E, Sherman EM, Vanmastigt R, Hamiwka L. Deterioration in cognitive function in children with benign epilepsy of childhood with centro temporal spikes treated with sulthiame. Journal of Child Neurology 2008; 23: 14–21.

the epilepsy prescriber’s guide to antiepileptic drugs

Tiagabine Therapeutics Chemical name and structure: Tiagabine   HCl,   R-n-(4,4-di(3-methyl-thien-2-yl)-but-3-enyl)nipecotic acid hydrochloride, is a white odorless crystalline powder, with a molecular weight of 375.5 and an empirical formula of C20H 25NO2S2 .

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therapeutics

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Generics available: • No Licensed indications for epilepsy: • Adjunctive treatment of partial seizures with or without secondary generalization in adults and children aged 12 years and above (UK-SPC; FDA-PI) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • Anxiety disorders • Neuropathic pain/chronic pain Ineffective (contraindicated): • Induces absence seizures • Provokes absence status epilepticus often ending in generalized tonic–clonic seizures

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Mechanism of action: • Selectively blocks reuptake of GABA by presynaptic and glial GABA transporter-1 (GAT-1) Efficacy profile: • The goal of treatment is complete remission of seizures • Continue treatment until all symptoms are gone or until improvement is stable and then continue treating indefinitely as long as improvement persists • Efficacy should be apparent within 2 weeks of treatment initiation • If it is not producing clinical benefits within 6–8 weeks, it may require a dosage increase or it may not work at all • If tiagabine is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Tiagabine

Pharmacokinetics Absorption and distribution: • Oral bioavailability: ≥ 90% • Food co-ingestion: delays the rate but does not decrease the extent of absorption • Tmax: 0.5–2 hours • Time to steady state: 1–2 days • Pharmacokinetics: linear • Protein binding: 96% • Volume of distribution: 1.0 L/kg • Salivary concentrations:  it is not known whether tiagabine is secreted into saliva and whether such concentrations are similar to the unbound levels seen in plasma Metabolism: • Metabolized in the liver, primarily by CYP3A4, to two 5-oxo­t iagabine isomers (E5 and Z-5) and represent ~60% of metabolism • The remaining 40% of metabolites have yet to be identified • The metabolites of tiagabine are not pharmacologically active • Autoinduction is not a feature of tiagabine metabolism

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Elimination: • During tiagabine monotherapy half-life values in adults are 5–9 hours • During tiagabine polytherapy with enzyme-inducing AEDs halflife values in adults are 2–4 hours • Renal excretion: 25% of tiagabine is eliminated in urine and < 2% of an administered dose is excreted unchanged; 63% of an administered dose is excreted in feces as metabolites

the epilepsy prescriber’s guide to antiepileptic drugs

Pharmacodynamic drug interactions: • Co-medication with vigabatrin: enhanced seizure control may occur • Co-medication with triazolam:  may slightly prolong the CNS depressant effect of triazolam

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Adverse effects

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on tiagabine: –– Carbamazepine, phenobarbital, phenytoin, and primidone can increase the clearance of tiagabine and decrease tiagabine plasma levels –– Valproic acid can displace tiagabine from its albumin protein binding sites in blood and increases free pharmacologically active tiagabine levels • Interactions between AEDs: effects by tiagabine: –– Tiagabine can decrease valproic acid plasma levels • Interactions between AEDs and non-AED drugs:  effects on tiagabine: –– Cimetidine can increase tiagabine plasma levels –– Naproxen and salicylic acid can displace tiagabine from its albumin protein binding sites in blood and increases free pharmacologically active tiagabine levels • Interactions between AEDs and non-AED drugs:  effects by tiagabine: –– To date, there have been no reports of tiagabine affecting the clearance of other non-AED drugs and affecting their plasma levels

Hormonal contraception: • Tiagabine does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control Adverse effects How drug causes adverse effects: • CNS adverse effects may be due to excessive actions of GABA Common adverse effects: • Sedation, dizziness, asthenia, nervousness • Depression, difficulty concentrating, speech/language problems, confusion, tremor • Nausea, vomiting, diarrhea • Ecchymosis (bruising) Life-threatening or dangerous adverse effects: • Concerns that tiagabine, like the GABAergic-acting vigabatrin, may cause visual field defects have not been substantiated • Suicidal ideation and behavior may occur

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Rare and not life-threatening adverse effects: • Delusion • Hallucinations Weight change: • Not common; weight gain reported but not expected What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Take more of the dose at night or all of the dose at night to reduce daytime sedation • Lower the dose

Tiagabine

Dosing and use Usual dosage range: • Adults: 30–45 mg/day (with enzyme-inducing AEDs) • Adults: 15–30 mg/day (without enzyme-inducing AEDs) • Children: 0.5–2 mg/kg/day Available formulations: • Tablets: 5 mg, 10 mg, 15 mg (UK) • Tablets: 2 mg, 4 mg, 12 mg, 16 mg (USA) How to dose: • When initiating tiagabine treatment start with a low dose and titrate slowly so as to minimize adverse effects –– For adults co-prescribed enzyme-inducing AEDs:  start treatment with 5–10 mg twice daily for 1 week; each week increase by 5–10 mg/day; maintenance dose generally 30–45 mg/day and at doses greater than 30 mg administration should be thrice daily –– For adults co-prescribed nonenzyme-inducing AEDs: start treatment with 5–10 mg twice daily for 1 week; each week increase by 5–10 mg/day; maintenance dose generally 15–30 mg/day –– Children over 12 years old:  start treatment with 0.1 mg/kg/day and titrate in increments of 0.1 mg/kg/day every 1 or 2 weeks; maintenance dose generally 0.5–2 mg/kg/day

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Dosing tips: • Because for a given dose patients on non–enzyme-inducing AEDs achieve tiagabine blood levels that are double that of patients receiving enzyme-inducing AEDs, these patients often require lower and less frequent doses of tiagabine; these patients may also require a slower titration schedule compared with that of induced patients

the epilepsy prescriber’s guide to antiepileptic drugs • Gastrointestinal absorption is markedly slowed by the concomitant intake of food, which also lessens peak plasma levels; thus, for improved tolerability and consistent therapeutic response, patients should be instructed to always take tiagabine with food • The manner of dose administration (high dosage, fast titration rate) may increase tiagabine-associated status epilepticus and new onset seizures

Overdose: • No fatalities have been reported (doses up to 720 mg); symptoms include:  coma, sedation, agitation, confusion, speech difficulty, hostility, depression, weakness, myoclonus, spike and wave stupor, tremors, vomiting • If indicated the stomach should be emptied by lavage or by induction of emesis • It is not known whether hemodialysis removes tiagabine from blood and, therefore, serves as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Before starting: blood count including platelet count, and liver and kidney function tests • During treatment: blood count including platelet count (particularly if bruising is observed), liver and kidney function tests every 6–12 months • Rare cases of visual field defects have been reported with tiagabine; if visual field symptoms develop the patient should be referred to an ophthalmologist for further evaluation including perimetry • Therapeutic drug monitoring: –– Overall, in patients treated with therapeutic doses of tiagabine, plasma tiagabine concentrations are in the order of 20–200 ng/mL (53–532 nmol/L) –– The conversion factor from ng/mL to nmol/L is 2.66 (i.e., 1 ng/L = 2.66 nmol/L) –– The reference range of tiagabine in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– There are no data indicating the usefulness of monitoring tiagabine by use of saliva

Dosing and use

How to withdraw drug: • There is no need to adjust dosage of concurrent medications as tiagabine is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • Taper: over a period of 2–3 weeks • Rapid discontinuation may increase the risk of withdrawal seizures

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Other warnings/precautions: • Some patients may experience dizziness and somnolence and thus caution needs to be exercised if patient intends to drive or use machinery • Accidental injury was an adverse effect that was reported by 2.8% of patients administered tiagabine during its clinical evaluation • Low white blood cell count (<2.5 × 109 per liter) was more frequent with tiagabine (4.1%) compared with placebo (1.5%) • Patients with a history of serious behavioral problems have an increased risk of recurrence of these symptoms Do not use: • If patient has a proven allergy to gabapentin or pregabalin or to any of the excipients: tablets contain lactose • Because formulation contains lactose, patients with rare hereditary problems of galactose intolerance, Lapp lactose deficiency, or glucose–galactose malabsorption should not take this medicine

Tiagabine

Special populations Renal impairment: • Although tiagabine undergoes moderate renal excretion, its pharmacokinetics are unaffected in patients with renal impairment, so the dose need not be changed Hepatic impairment: • Tiagabine is extensively metabolized and consequently lower doses and/or reduced dose intervals should be used and patients should be monitored closely for adverse effects such as dizziness and tiredness • In patients with mild to moderate hepatic impairment (Child Pugh Score 5–9) the initial daily maintenance dose should be 5–10 mg administered twice daily • Tiagabine should not be used in patients with severe hepatic impairment Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults • There is no experience with tiagabine in children under the age of 12 years and, therefore, tiagabine should not be used in this age group

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Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better

the epilepsy prescriber’s guide to antiepileptic drugs • Because of an age-related reduction in renal and hepatic function, lower tiagabine doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions is high, particularly with those drugs that inhibit/induce CYP3A4, the primary isoenzyme responsible for the metabolism of tiagabine

Tiagabine, overall role

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Tiagabine is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than tiagabine monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • Data on the pharmacokinetic changes of tiagabine during pregnancy are not available. However, because tiagabine is highly protein bound (96%) and its elimination is the consequence of extensive metabolism, significant changes in the pharmacokinetics of tiagabine can be expected during pregnancy

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Breast feeding • Breast milk:  it is not known whether tiagabine is excreted into breast milk • Breastfed infants: it is not known what plasma tiagabine concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed The overall place of tiagabine in the treatment of epilepsy The efficacy of tiagabine is limited to focal seizures and its role is limited to adjunctive medication in severe forms of focal seizures that failed to respond to other antiepileptic drug combinations. It may also be effective in epileptic spasms of epileptic encephalopathies.

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Primary seizure types: • Severe focal epilepsies with or without secondarily generalized tonic–clonic seizures Secondary seizure types: • None Potential advantages: • Does not affect the pharmacokinetics of other drugs

Tiagabine

Potential disadvantages: • Narrow spectrum of efficacy against focal seizures only • It is a pro-absence drug; its use is prohibited in idiopathic generalized epilepsy with absences • May require two–four times a day dosing • Needs to be taken with food • Associated with significant pharmacokinetic interactions in that its metabolism is readily induced • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Ben-Menachem E. International experience with tiagabine add-on therapy. Epilepsia 1995; 36(Suppl 6): S14-S21. Brodie MJ. Tiagabine pharmacology in profile. Epilepsia 1995; 36(Suppl 6): S7-S9. Brodie MJ. Tiagabine in the management of epilepsy. Epilepsia 1997; 38(Suppl 2): S23-S27. Leppik IE. Tiagabine: the safety landscape. Epilepsia 1995; 36 (Suppl 6): S10–S13. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. So EJ, Wolff D, Graves NM, Leppik IE, Cascino GD, Pixton GC, Gustavson LE. Pharmacokinetics of tiagabine as add-on therapy in patients taking enzyme-inducing antiepilepsy drugs. Epilepsy Research 1995; 22: 221–226. Uthman BM, Rowan J, Ahmann PA, Leppik IE, Schachter SC, Sommerville KW, Shu V. Tiagabine for complex partial seizures. A randomized, add-on, dose-response trial. Archives of Neurology 1998; 55: 56–62. Walker MC. The mechanism of action of tiagabine. Reviews in Con­ temporary Pharmacotherapy 2002; 12: 213–224. Wang X, Patsalos PN. The pharmacokinetic profile of tiagabine. Reviews in Contemporary Pharmacotherapy 2002; 12: 225–234. 262

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Topiramate Therapeutics Chemical name and structure: Topiramate, 2,3:4,5-bis-O-(1-methylethylidene)-β-D-fructopyranose sulfamate, is a sulfamate-substituted monosaccharide derived from the D-enantiomer of fructose. Its molecular weight is 339.37, and its empirical formula is C12H21NO8S.

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O O

O

O

O

NH2

O

O

Brand names: • Epilramate; Epitomax; Epitop • Gabatopa • Topamac; Topamax; Topamax Sprinkle; Topimax; Topinmate; Topirid; Topitrim; Topomac

THERAPEUTICS

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S

Generics available: • Yes Licensed indications for epilepsy: • Monotherapy (in patients 10 years or older) or adjunctive therapy (in patients 2 years or older) of partial and secondarily generalized seizures (FDA-PI) • Monotherapy (in patients 10 years or older) or adjunctive therapy (in patients 2 years or older) of primary generalized tonic–clonic seizures in patients 10 years or older (FDA-PI) • Adjunctive treatment of seizures associated with Lennox-Gastaut syndrome in patients 2 years or older (FDA-PI) • Monotherapy in adults and children aged 6 years and above with newly diagnosed epilepsy who have generalized tonic–clonic seizures or partial seizures with or without secondarily generalized seizures (UK-SPC) • Adjunctive therapy for adults and children over 2 years of age who are inadequately controlled on conventional first line antiepileptic drugs for partial seizures with or without secondarily generalized seizures, seizures associated with Lennox-Gastaut syndrome and for primary generalized tonic–clonic seizures (UK-SPC) Licensed indications for non-epilepsy conditions: • Migraine prophylaxis in adults (UK-SPC; FDA-PI)

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Nonlicensed use for epilepsy: • Absence seizures • Infantile spasms (West syndrome) • Juvenile myoclonic epilepsy • Myoclonic astatic epilepsy (Doose syndrome) • Progressive myoclonic epilepsy • Severe myoclonic epilepsy of infancy (Dravet syndrome) Nonlicensed use for non-epilepsy conditions: • Bipolar disorder • Post-traumatic stress disorder • Psychotropic drug-induced weight gain • Binge-eating disorder • Cluster headaches • Neuropathic pain

Topiramate

Ineffective (contraindicated): • Topiramate is potentially effective against all seizure types and is not contraindicated for any seizure type or epilepsy Mechanism of action: • Enhances GABA-mediated inhibition • Inhibits voltage-dependent sodium channels • Enhances potassium channel conduction • Inhibition of L-type high voltage-activated calcium channels • Decreases glutamate-mediated excitatory neurotransmission • Carbonic anhydrase inhibition, but the potency of topiramate is much lower than that of acetazolamide; topiramate probably does not exert its anticonvulsant effect through inhibition of carbonic anhydrase, but this mechanism may cause some of the clinical adverse effects Efficacy profile: • The goal of treatment is complete remission of seizures • Therapeutic effect usually evident within 2–4 weeks • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • No unusual incidence of loss of efficacy • If topiramate is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

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Pharmacokinetics Absorption and distribution: • Oral bioavailability: >80% • Food co-ingestion:  neither delays the rate of absorption nor decreases the extent of absorption • Tmax: 2–4 hours • Time to steady state: 4–5 days

the epilepsy prescriber’s guide to antiepileptic drugs • Pharmacokinetics: linear • Protein binding: 15% • Volume of distribution: 0.6–0.8 L/kg • Salivary concentrations: topiramate is secreted into saliva and concentrations are similar to the unbound levels seen in plasma

Elimination: • During maintenance topiramate monotherapy half-life values in adults are 20–30 hours • Compared with adults, the clearance is approximately 50% higher in older children and twice the adult value in infants • During maintenance topiramate polytherapy with enzyme­inducing AEDs half-life values in adults are 10–15 hours • Renal excretion: ~20–60% of an administered topiramate dose is eliminated in urine as unchanged topiramate Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on topiramate: –– Carbamazepine, oxcarbazepine, phenobarbital, phenytoin, primidone, and valproic acid can increase the clearance of topiramate and decrease topiramate plasma levels • Interactions between AEDs: effects by topiramate: –– Topiramate can decrease the clearance of phenytoin and increase phenytoin plasma levels –– Topiramate can increase the clearance of valproic acid and decrease valproic acid plasma level • Interactions between AEDs and non-AED drugs:  effects on topiramate: –– Amitriptyline, lithium, metformin, propranolol, and sumatriptan can decrease the clearance of topiramate and increase topiramate plasma levels

Drug interaction profile

Metabolism: • Topiramate is not extensively metabolized in patients on monotherapy or in patients not prescribed enzyme-inducing AEDs and typically 40–50% of a topiramate dose is excreted unchanged by means of the kidneys • In the presence of enzyme-inducing AEDs this value is doubled • Metabolites thus far identified include two hydroxy and two diol metabolites as well as several glucuronide conjugates, none of which constitutes more than 5% of an administered dose • Although the specific CYP isoenzymes for the metabolism of topiramate have not been identified, it is evident that isoenzymes induced by carbamazepine and phenytoin play a major role • Metabolites are not pharmacologically active • Topiramate may undergo tubular reabsorption • Autoinduction is not a feature of topiramate metabolism

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• Interactions between AEDs and non-AED drugs:  effects by topiramate: –– Topiramate can increase the clearance and decrease the plasma levels of digoxin, glibenclamide, pioglitazone, risperidone, and sumatriptan –– Topiramate can decrease the clearance and increase the plasma levels of amitriptyline, haloperidol, hydrochlorothiazide, lithium, and metformin

Topiramate

Pharmacodynamic drug interactions: • Topiramate may enhance the risk of valproate-associated adverse effects, including elevated ammonium, hyperammonemic encephalopathy, elevated transaminases, apathy, and hypothermia • It has been proposed that the hyperammonemic encephalopathy may be due to an increase in the presence of topiramate of a potentially toxic metabolite of valproate, 4-ene-valproate • Symptoms of decreased appetite, weight loss and nervousness by topiramate can be exacerbated by levetiracetam particularly in children • Topiramate may interact with other carbonic anhydrase inhibitors (e.g., acetazolamide, sulthiame, zonisamide) to increase the risk of kidney stones Hormonal contraception: • Topiramate enhances the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and to reduce their effectiveness, leading to breakthrough bleeding and contraceptive failure; medium- or high-dose oral contraceptive preparations are indicated in patients taking topiramate Adverse effects How drug causes adverse effects: • Mechanism by which topiramate causes adverse effects has not been established • Carbonic anhydrase inhibition by topiramate, although not or only minimally involved in its antiepileptic activity, may be the mechanism responsible for some of the clinical adverse effects, such as metabolic acidosis, paresthesias, kidney stones, and hypohydrosis

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Common adverse effects: • Psychomotor slowing • Fatigue • Change in cognition • Impairment of language and verbal memory, slurred speech • Decreased attention, change in behavior and mood • CNS-related adverse effects are often not dose-dependent but they are reversible

the epilepsy prescriber’s guide to antiepileptic drugs • Anorexia, nausea, taste perversion, and weight loss • Metabolic acidosis (lowered serum bicarbonate or CO2 , especially in children) • Hypohydrosis (decreased sweating, especially in children, may lead to hyperthermia) • Sedation, asthenia, dizziness, ataxia, nervousness, nystagmus, tremor • Blurred or double vision

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Life-threatening or dangerous adverse effects: • Metabolic acidosis • Oligohydrosis and hyperthermia (more common in children)

Weight change: • Weight loss is common; usually seen within 3 months and with a peak effect within 12–18 months, is dose related with more weight loss at high doses (mean, 6.5 kg or 7.3% decline) and less weight loss at lower doses (mean, 1.6 kg or 2.5% decline) What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Discuss symptoms associated with kidney stones, glaucoma, and hypohydrosis • Some CNS-related adverse effects may be lessened by slow titration, but they may persist at low doses despite slow titration • Cognitive adverse effects may be pronounced in some patients, but totally absent even at relatively high doses in others • Metabolic acidosis is usually compensated, but patients may be treated with oral bicarbonate for CO2 values of 15–18 mEq/L or less • If possible, topiramate should not be administered to patients on acetazolamide, sulthiame, zonisamide, or on the ketogenic diet, because these treatments also predispose to metabolic acidosis and to kidney stones • Patients should be encouraged to drink liberally while on topiramate to reduce the risk of kidney stones • Anorexia and weight loss may improve with dosage reduction • Children who benefit from topiramate treatment but experience hypohydrosis may experience improved heat tolerance after being sponged down or wrapped in a wet towel

Adverse effects

Rare and not life-threatening adverse effects: • Nephrolithiasis (1–2%) • Paresthesias, mostly tingling in the fingers and toes • Acute bilateral secondary narrow angle-closure glaucoma • Enhancement of the risk of valproate-associated hyperammonemic encephalopathy

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Dosing and use Usual dosage range: • Adults: 200–400 mg/day (without enzyme-inducing AEDs) • Adults: 400–600 mg/day (with enzyme-inducing AEDs) • Children (2–16 years): 3 mg/kg/day (monotherapy) • Children (2–16 years): 6–9 mg/kg/day (with enzyme inducing AEDs) Available formulations: • Tablets: 25 mg, 50 mg, 100 mg, 200 mg • Sprinkle capsules: 15 mg, 25 mg, 50 mg

Topiramate

How to dose: –– For adults and children over 12 years of age:  start treatment with 25–50 mg/day, twice daily; at intervals of 1–2 weeks increase as needed and as tolerated by 25–50 mg/day; maintenance dose generally 100–600 mg/day –– Children less than 12 years and infants: start treatment with approximately 0.5–1.0 mg/kg/day, two or three times daily; at intervals of 1–2 weeks increase as needed and as tolerated by approximately 0.5–1.0 mg/kg/day; maintenance dose generally 3–9 mg/kg/ day; doses of > 20 mg/kg/day may be necessary and well tolerated, especially in infants; dosage requirements increase two-fold in children co-prescribed enzyme-inducing AEDs Dosing tips: • Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating effects • Some patients may do very well at relatively low doses of topiramate, such as 100 mg/day in adults or 2–3 mg/kg/day in children; the response to treatment should be assessed at these doses before increasing the dose further • If there has been no evidence of seizure reduction at doses of 10–15 mg/kg/day in children, increasing the dose further is unlikely to be beneficial, but if there has been a gradual reduction in the seizure frequency, further dosage increases may be beneficial and well tolerated • Topiramate is available in a sprinkle capsule formulation, which can be swallowed whole or sprinkled over approximately a teaspoon of soft food (e.g., apple sauce); the mixture should be consumed immediately

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How to withdraw drug: • May need to adjust dosage of concurrent medications as topiramate is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • No data are available on potential for withdrawal seizures or symptoms upon rapid discontinuation

the epilepsy prescriber’s guide to antiepileptic drugs • Rapid discontinuation may increase the risk of seizures • If possible, taper dose over a period of 1–3 months • Women who are taking a medium- or high-dose oral contraceptive preparations while on topiramate can be switched to a regular contraceptive if they are not taking another enzyme-inducing AED

Tests and therapeutic drug monitoring: • Baseline and periodic (every 3–6 months) serum bicarbonate levels to monitor for hyperchloremic, nonanion gap metabolic acidosis (i.e., decreased serum bicarbonate below the normal reference range in the absence of chronic respiratory alkalosis) • Other routine laboratory testing is not necessary • During treatment: blood count and liver function tests at the latest after 2 months, then at least every 6 months throughout treatment • Therapeutic drug monitoring: –– Optimum seizure control in adult patients on monotherapy is most likely to occur at topiramate plasma concentrations of 5–20 mg/L (15–59 μmol/L) –– Optimum seizure control in children aged 6–12 years on topiramate monotherapy is most likely to occur at topiramate plasma concentrations of 2–21 mg/L (6–59 μmol/L) –– Optimum seizure control in children 5 years and younger on topiramate monotherapy is most likely to occur at topiramate plasma concentrations of 3–29 mg/L (9–86 μmol/L) –– The conversion factor from mg/L to μmol/L is 2.95 (i.e., 1 mg/L = 2.95 μmol/L) –– Topiramate can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant

Dosing and use

Overdose: • A patient who ingested 96–110 g of topiramate was admitted to hospital with coma lasting 20–24 hours followed by full recovery after 3–4 days; another patient who ingested 8,000 mg of topiramate was admitted to hospital with nonconvulsive status epilepticus but fully recovered after being administered 4 mg of lorazepam iv. • Signs and symptoms of topiramate overdoses include:  severe metabolic acidosis, convulsions, drowsiness, speech disturbance, blurred vision, diplopia, impaired mentation, lethargy, abnormal coordination, stupor, hypotension, abdominal pain, agitation, dizziness, and depression • Deaths have been reported after poly-drug overdoses involving topiramate • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes topiramate from blood and, therefore, serves as a useful procedure in cases of overdose

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Other warnings/precautions: • Patients should be monitored carefully for evidence of cognitive adverse effects • Patients should be monitored carefully for evidence of kidney stones • If symptoms of metabolic acidosis develop (hyperventilation, fatigue, anorexia, cardiac arrhythmias, stupor) then dose may need to be reduced or treatment may need to be discontinued • Depressive effects may be increased by other CNS depressants (alcohol, MAOIs, other AEDs, etc.) • Use with caution when combining with other drugs that predispose patients to heat-related disorders, including carbonic anhydrase inhibitors and anticholinergics

Topiramate

Do not use: • Use with great caution in patients undergoing treatments that are associated with an increase in risk of kidney stones, such as acetazolamide, sulthiame, zonisamide, and the ketogenic diet • Use with caution in patients taking valproic acid

Special populations Renal impairment: • Topiramate is renally excreted and consequently lower doses may be required • In renal failure (CrCL < 30 mL/min/1.73 m 2) approximately 50% of the usual dose is recommended • After hemodialysis, an additional dose (approximately half of the daily dose, in addition to the full daily dose) of topiramate may be necessary, because topiramate is cleared from plasma during dialysis at a rate which is approximately nine times higher than in patients with normal renal function Hepatic impairment: • Topiramate is extensively metabolized in the liver (particularly when co-prescribed with enzyme-inducing AEDs) and consequently lower doses may be required

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Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults • It appears that children are at higher risk of developing metabolic acidosis as well as symptoms related to hypohydrosis

the epilepsy prescriber’s guide to antiepileptic drugs Elderly: • Elderly patients are more susceptible to adverse effects (especially somnolence) and, therefore, often do better at lower doses • Because of an age-related reduction in renal and hepatic function, lower topiramate doses may be appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with topiramate is substantial

Topiramate, overall role

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Topiramate is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than topiramate monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • During pregnancy, topiramate pharmacokinetics change significantly so that topiramate plasma concentrations decrease by ~40% due to increased clearance; an increase in topiramate dose may be required in some patients

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Breast feeding • Breast milk: 70–110% of maternal plasma levels • Breastfed infants: topiramate plasma levels are 9–17% of maternal plasma levels • If drug is continued while breast feeding, infant should be monitored for possible adverse effects (irritability or sedation) • If adverse effects are observed recommend bottle feed

The overall place of topiramate in the treatment of epilepsy Topiramate is a broad spectrum antiepileptic drug and is a second line therapy in partial epilepsies and idiopathic generalized epilepsies with generalized tonic–clonic seizures, as well as juvenile myoclonic epilepsy. It has a particular place in the treatment of apparently

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resistant partial epilepsy and symptomatic generalized epilepsies where other antiepileptic drugs have been shown to be ineffective or contraindicated. Topiramate is a drug of first or second choice in patients with the Lennox-Gastaut syndrome. Primary seizure types: • Partial seizure • Idiopathic generalized seizures (with generalized tonic–clonic seizures, as well as juvenile myoclonic epilepsy) • Lennox-Gastaut syndrome

Topiramate

Secondary seizure types: • Juvenile myoclonic epilepsy • Infantile spasms (West syndrome) • Severe myoclonic epilepsy of infancy (Dravet syndrome) • Myoclonic astatic epilepsy (Doose syndrome) • Absence seizures • Progressive myoclonic epilepsy Potential advantages: • Topiramate has a broad spectrum of seizure protection and is not associated with seizure aggravation • Demonstrates a favorable pharmacokinetic profile with linear kinetics • Topiramate has a well-defined adverse event profile with virtually no life-threatening adverse effects and no irreversible adverse effects Potential disadvantages: • The main limitation for the use of topiramate has been its negative effect on cognitive functions • Has several potential adverse effects • Problematic for patients with a history of kidney stones or risks for metabolic acidosis • Children may suffer from predictable detrimental reductions in growth rate and bone-related sequelae in long-term use • Associated with significant pharmacokinetic interactions • Potential teratogen, but not more than most other antiepileptic drugs

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Suggested reading Ben-Menachem E, Axelsen M, Johanson EH, Stagge A, Smith U. Predictors of weight loss in adults with topiramate-treated epilepsy. Obesity Research 2003; 11: 556–562. Biton V, Bourgeois BF. Topiramate in patients with juvenile myoclonic epilepsy. Archives of Neurology 2005; 62: 1705–1708. Biton V, Montouris GD, Ritter F, Riviello JJ, Reife R, Lim P, Pledger G. A randomized, placebo-controlled study of topiramate

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Topiramate, overall role

in primary generalized tonic-clonic seizures. Topiramate YTC Study Group. Neurology 1999; 52: 1330–1337. Faught E, Wilder BJ, Ramsay RE, Reife RA, Kramer LD, Pledger GW, Karim RM. Topiramate placebo-controlled dose-ranging trial in refractory partial epilepsy using 200-, 400-, and 600-mg daily dosages. Topiramate YD Study Group. Neurology 1996; 46: 1684–1690. Glauser TA, Clark PO, Strawsburg R. A pilot study of topiramate in the treatment of infantile spasms. Epilepsia 1998; 39: 1324–1328. Groeper K, McCann ME. Topiramate and metabolic acidosis: a case series and review of the literature. Paediatric Anaesthesia 2005; 15: 167–170. Hamer HM, Knake S, Schomburg U, Rosenow F. Valproate-induced hyperammonemic encephalopathy in the presence of topiramate. Neurology 2000; 54: 230–232. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. Meador KJ, Loring DW, Hulihan JF, Kamin M, Karim R. Differential cognitive and behavioral effects of topiramate and valproate. Neurology 2003; 60: 1483–1488. Meador KJ, Loring DW, Vahle VJ, Ray PG, Werz MA, Fessler AJ, Ogrocki P, Schoenberg MR, Miller JM, Kustra RP. Cognitive and behavioral effects of lamotrigine and topiramate in healthy volunteers. Neurology 2005; 64: 2108–2114. Mirza N, Marson AG, Pirmohamed M. Effect of topiramate on acid-base balance: extent, mechanism and effects. British Journal of Clinical Pharmacology 2009; 68: 655–661. Mula M, Trimble MR, Thompson P, Sander JW. Topiramate and word-finding difficulties in patients with epilepsy. Neurology 2003; 60: 1104–1107. Ohman I, Sabers A, de Flon P, Luef G, Tomson T. Pharmacokinetics of topiramate during pregnancy. Epilepsy Research 2009; 87: 124–129. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Privitera M, Fincham R, Penry J, Reife R, Kramer L, Pledger G, Karim R. Topiramate placebo-controlled dose-ranging trial in refractory partial epilepsy using 600-, 800-, and 1,000-mg daily dosages. Topiramate YE Study Group. Neurology 1996; 46: 1678–1683. Sachdeo RC, Glauser TA, Ritter F, Reife R, Lim P, Pledger G. A double-blind, randomized trial of topiramate in LennoxGastaut syndrome. Neurology 1999; 52: 1882–1887.

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Valproate Therapeutics Chemical name and structure: Valproic acid, N-dipropylacetic acid, is a short-chain branched fatty acid that occurs as a colorless liquid, with a molecular weight of 144.21 and an empirical formula of C8H16O2 . Because most formulations are salts (e.g., sodium valproate, magnesium valproate, and sodium divalproate), valproic acid is often called valproate. COOH

Valproate

Brand names: • Absenor; Apilepsin • Convulex • Depacon; Dapakan; Depakene; Depakene-R; Depakin; Depakine; Depakine Chrono; Depakote; Depakote ER; Depakote Sprinkles; Depalept; Depalept Chrono; Depamag; Deprakine; Deproic; Desorate; Diproex ER; Dipromal Divalproex • Epilex; Epilim; Epilim Chrono; Epilim Chronosphere; Episenta; Epival; Ergenyl; Everiden • Leptilan; Logical; Logical Jarabe • Orfiril; Orfiril Retard • Petilin; Pragmaten • Valcote; Valpakine; Valparin; Valporal; Valprax; Valpro; Vematina; Vupral Generics available: • Yes Licensed indications for epilepsy: • Complex partial seizures that occur either in isolation or in association with other types of seizures (monotherapy and adjunctive) (FDA-PI) • Simple and complex absence seizures (monotherapy and adjunctive) (FDA-PI) • Multiple seizure types which include absence seizures (adjunctive) (FDA-PI) • Monotherapy or adjunctive therapy for any form of epilepsy in patients of any age (UK-SPC)

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Licensed indications for non-epilepsy conditions: • Migraine prophylaxis (divalproex, divalproex ER) (FDA-PI) • Mania (divalproex only) (FDA-PI)

the epilepsy prescriber’s guide to antiepileptic drugs Nonlicensed use for epilepsy: • Febrile seizures • Infantile spasms (West syndrome) • Juvenile myoclonic epilepsy • Lennox-Gastaut syndrome • Neonatal seizures • Refractory status epilepticus

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Nonlicensed use for non-epilepsy conditions: • Bipolar depression • Psychosis, schizophrenia (adjunctive)

Mechanism of action: • Raises brain levels of GABA, possibly through inhibition of GABAtransaminase, or through inhibition of succinic semialdehyde dehydrogenase, or through an increase in glutamic acid decarboxylase activity; these changes occur at higher than usual therapeutic doses and their time course lags behind the anticonvulsant effect • Can reduce sustained repetitive high-frequency firing by blocking voltage-sensitive sodium channels or by activating calciumdependent potassium conductance • Decreases brain levels of the excitatory amino acid aspartate • Decreases the expression of hippocampal glutamate transporter-1 • None of the identified actions are widely accepted as the predominant relevant mechanism

Pharmacokinetics

Ineffective (contraindicated): • Valproic acid is potentially effective against all seizure types and is not contraindicated for any seizure type or epilepsy • Adverse effect profile may not justify use for prophylaxis of febrile seizures

Efficacy profile: • The goal of treatment is complete remission of seizures • Onset of action may occur within a few days, but maximal efficacy may not be seen until several weeks after initiation of therapy • Goal of therapy in idiopathic generalized epilepsies is not only full seizure control, but also normalization of EEG • No unusual incidence of loss of efficacy • If ineffective or only partially effective, consider replacing by or co-prescribing with lamotrigine, ethosuximide, levetiracetam, topiramate, or zonisamide for generalized epilepsies, or another appropriate drug in patients with focal onset seizures Pharmacokinetics Absorption and distribution: • Oral bioavailability:  >90% (8–20% lower for extended release formulations)

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• Food co-ingestion: delays the rate of absorption but has no effect on the extent of absorption • Tmax: 1–2 hours (syrup and uncoated immediate release tablets); 3–7 hours (enteric coated tablets and sprinkles); extended release formulations have prolonged Tmax values • Time to steady state: 2–4 days • Pharmacokinetics: nonlinear due to saturable protein binding • Protein binding: 90%; saturable at therapeutic concentrations: free (unbound) fraction 7% at 50 mg/L, 9% at 75 mg/L, 15% at 100 mg/L, 22% at 125 mg/L, and 30% at 150 mg/L • The free fraction of valproic acid is also higher in newborns, as well as in the elderly • Volume of distribution: 0.13–0.19 L/kg (adults); 0.20–0.30 L/kg (children) • Salivary concentrations:  valproic acid is secreted into saliva but concentrations do not reflect the unbound levels seen in plasma Metabolism: • The metabolism of valproic acid in the liver is extensive and complex in that it involves multiple metabolic pathways including O-glucuronidation, β-oxidation, omega-oxidation, hydroxylation, ketone formation, and desaturation • To date in excess of 25 metabolites have been identified • Valproic acid glucuronide and 3-oxo-valproic acid are by far the most abundant metabolites (~40% and 33% of an administered dose respectively) • Hydroxylation to form 4-ene-valproic acid and other metabolites is by means of the action of CYP2A6, CYP2C9, CYP2C19, and CYP2B6 isoenzymes whereas O-glucuronidation is mediated by UGT1A3 and UGT2B7 isoforms • Some metabolites are pharmacologically active; 2-ene-valproic acid and 4-ene-valproic acid have anticonvulsant activity that is similar in potency to that of valproic acid itself • Autoinduction is not a feature of valproic acid metabolism Elimination: • In the absence of enzyme-inducing AEDs, half-life values for valproic acid in adults are 12–16 hours • In the presence of enzyme-inducing AEDs, half-life values for valproic acid in adults are 5–9 hours • In the absence of enzyme-inducing AEDs in children, half-life values are 8.4–12.5 hours in infants, and 8.6–12.3 hours in older children • In the presence of enzyme-inducing AEDs in children, half-life values are 4–8 hours in infants, and 7–9.4 hours in older children • Newborns eliminate valproic acid slowly, with half-life values of 20–40 hours

the epilepsy prescriber’s guide to antiepileptic drugs • Renal excretion:  ~97% of an administered dose is excreted as metabolites in urine; 40% as valproic acid glucuronide and 33% as 3-oxo-valproic acid; 20% comprise ~22 other minor metabolites • Renal excretion:  1–3% of an administered dose is excreted as unchanged valproic acid in urine

Drug interaction profile

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on valproic acid: –– Carbamazepine, lamotrigine, phenobarbital, phenytoin, primidone, and topiramate can increase the clearance of valproic acid and decrease valproic acid plasma levels –– Ethosuximide can decrease valproic acid plasma levels by means of an unknown mechanism –– Clobazam, felbamate, and stiripentol can decrease the clearance of valproic acid and increase valproic acid plasma levels • Interactions between AEDs: effects by valproic acid: –– Valproic acid can decrease the clearance and increase plasma levels of carbamazepine-10,11-epoxide (active metabolite of carbamazepine), ethosuximide, felbamate, lamotrigine, lorazepam, midazolam, phenobarbital, and rufinamide –– Valproic acid can increase the clearance and decrease plasma levels of topiramate and zonisamide –– Valproic acid can increase the free fraction of phenytoin by displacing phenytoin from its plasma protein (albumin) binding site and by a concurrent inhibition of phenytoin clearance –– Valproic acid can increase the free fraction of 10-hydroxycarbazepine (pharmacologically active metabolite of oxcarbazepine) and diazepam by displacing them from their plasma protein (albumin) binding sites • Interactions between AEDs and non-AED drugs: effects on valproic acid: –– Amikacin, diflunisal, meropenem, naproxen, paripenem, rifampicin, and ritonavir can increase the clearance and decrease valproic acid plasma levels –– Oral contraceptives can increase the clearance of valproic acid and decrease valproic acid plasma levels –– Acyclovir, cisplatin, and methotrexate can decrease valproic acid plasma levels by means of an unknown mechanism –– Chlorpromazine, fluoxetine, isoniazid, and sertraline can decrease the clearance and increase valproic acid plasma levels –– Acetylsalicylic acid can increase the free fraction of valproic acid by displacing valproic acid from its plasma protein (albumin) binding site and by a concurrent inhibition of valproic acid clearance

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• Interactions between AEDs and non-AED drugs:  effects by valproic acid: –– Valproic acid can decrease the clearance and increase the plasma level of amitryptyline, aripiprazole, clomipramine, chlorpromazine, lopinavir, naproxen, nimodipine, nortriptyline, paroxetine, and zidovudine

Valproate

Pharmacodynamic drug interactions: • Patients who fail to respond to maximally tolerated doses of either valproic acid or lamotrigine alone can achieve better seizure control when the two agents are combined. This pharmacodynamic interaction also entails a risk of reciprocal potentiation of adverse effects, particularly tremor, and a reduction in the dosage of both drugs is usually required • The combination of ethosuximide with valproic acid can also lead to a favorable pharmacodynamic interaction which may allow the control of absence seizures in patients not responsive to monotherapy with either drug • Use of valproate with clonazepam may cause absence status • Valproic acid in combination with lithium is associated with a pharmacodynamic interaction leading to lithium neurotoxicity • Valproic acid in combination with cisplatin is associated with three-fold higher incidence of thrombopenia, neutropenia, or both; this is considered to be a consequence of a pharmacodynamic interaction Hormonal contraception: • Valproic acid does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects How drug causes adverse effects: • Mechanism by which valproic acid causes adverse effects has not been established, but CNS adverse effects are likely due to same mechanism as seizure protection • Metabolite 4-ene-valproic acid has pronounced embryotoxicity and hepatotoxicity

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Common adverse effects: • Tremor, drowsiness, lethargy, dizziness, ataxia, asthenia, headache • Nausea, vomiting, anorexia, constipation, dyspepsia, diarrhea, gastrointestinal distress • Alopecia • Hyperammonemia • Hypocarnitinemia • Decreased bone mineral density

the epilepsy prescriber’s guide to antiepileptic drugs Life-threatening or dangerous adverse effects: • Rare hepatotoxicity with liver failure sometimes severe and fatal, particularly in children under 2 years of age • Rare pancreatitis, sometimes fatal • Reversible dementia, brain atrophy, encephalopathy, extrapyramidal symptoms • Neutropenia, bone marrow suppression

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Rare and not life-threatening adverse effects: • Facial and limb edema • Nocturnal enuresis • Hyperinsulinism (debated) • Menstrual irregularities (debated) • Polycystic ovaries (controversial)

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • CNS-related adverse effects are usually dose-dependent and are reversible • Risk of serious adverse effects is greatest in the first few months of treatment • Thrombocytopenia is usually dose-related and platelet counts between 100,000 and 200,000 are common and can be monitored without intervention • Tremor may improve with dosage reduction and with propranolol treatment • Mild to moderate hyperammonemia is usually asymptomatic and does require intervention • L-carnitine supplementation is strongly suggested in the following groups of patients:  those with certain secondary carnitine deficiency syndromes, symptomatic valproic acid-associated hyperammonemia, multiple risk factors for valproic acid hepatotoxicity or renal-associated syndromes, infants and young children taking valproic acid, patients with epilepsy using the ketogenic diet who have hypocarnitinemia, patients receiving dialysis, and premature infants who are receiving total parenteral nutrition • Consider calcium (600–1000 mg/day) and vitamin D supplements (2000 IU/day) in cases of decreased bone mineral density • Obtain liver function tests in cases of symptoms suggestive of valproic acid hepatotoxicity, which include nausea, vomiting, anorexia, lethargy, jaundice, edema, and at times loss of seizure control • Obtain serum amylase and lipase in cases of symptoms suggestive of pancreatitis, which include mostly vomiting and abdominal pain

Adverse effects

Weight change: • Weight gain is common; can be a health problem in some patients with weight gains up to 50 kg reported

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• Multivitamins fortified with zinc and selenium may help reduce alopecia • Sedation can be problematic and not tolerated by some patients; can wear off over time but can re-emerge as dose increases and then wear off again over time

Dosing and use Usual dosage range: • Adults: 500–2500 mg/day • Children under 20 kg: 20–40 mg/kg/day • Children over 20 kg: 20–30 mg/kg/day

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Available formulations: • Enteric-coated tablets: 200 mg, 500 mg • Crushable tablets: 100 mg • Capsules: 150 mg, 300 mg, 500 mg • Solution (sugar-free) or syrup: 200 mg/5 mL, 250 mg/5 mL • Sustained-release tablets: 200 mg, 300 mg, 500 mg • Sustained-release microspheres, sachets: 50 mg, 100 mg, 250 mg, 500 mg, 750 mg, 1000 mg • Divalproex tablets:  125 mg, 300 mg, 500 mg (as valproic acid equivalents) • Divalproex tablets delayed release:  125 mg, 250 mg, 500 mg (as valproic acid equivalents) • Divalproex sprinkles: 125 mg (as valproic acid equivalents) • Divalproex tablets extended release: 250 mg, 500 mg (as valproic acid equivalents) • Chronospheres [modified release granules]: 500 mg (sodium valproate, 333.30 mg; valproic acid 145.14 mg; overall equivalent to 500 mg sodium valproate) • Solution for intravenous injection: 100 mg/mL (5 mL vial) How to dose: –– For adults and children over 12 years of age: start treatment with 500 mg/day, twice daily; at intervals of 5–7 days increase as needed and as tolerated by 500 mg/day; maintenance dose generally 1000–2500 mg/day –– Children:  start treatment with approximately 15 mg/kg/day, twice daily or three times daily; at intervals of 5–7 days increase as needed and as tolerated by upto 15 mg/kg/day; maintenance dose generally 20–30 mg/kg/day; doses of up to 100 mg/ kg/day may be necessary, especially in younger children; dosage requirements increase two-fold in children co-prescribed enzyme-inducing AEDs

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Dosing and use

Dosing tips: • Higher peak valproic acid levels occur with the regular enteric coated and suspension formulation than with the same dose of the extended release formulation • Regular enteric coated formulations are not extended release but merely delayed release formulations; absorption of valproic acid is delayed but rapid • Use enteric coated formulation to avoid gastrointestinal effects • Do not break or chew enteric coated tablets as this will defeat the purpose of the enteric coating • Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating effects • Daily doses of the extended release formulations should be 8–20% higher than for the other formulations to achieve the same plasma levels of valproic acid because of the slightly reduced bioavailability of the extended release formulations • Given the half-life of immediate release valproate (e.g, Depakene, Depakote), twice daily dosing is probably ideal • Extended release valproate (e.g., Depakote ER) can be given once daily • However, extended release valproate is only 80% as bioavailable as immediate release valproate, producing plasma drug levels 10–20% lower than with immediate release valproate • Thus, the dose of extended release valproate may need to be higher (by approximately one-third) when converting patients to ER formulation • Divalproex ER improves gastrointestinal adverse effects and alopecia compared with immediate release Divalproex or generic valproate • The amide of valproic acid is available in Europe [valpromide (Depamide)] and has a more profound interaction with ­carbamazepine-epoxide compared with other formulations How to withdraw drug: • May need to adjust dosage of concurrent medications as valproic acid is being discontinued, because plasma levels of other drugs may change (see Pharmacokinetic drug interactions section) • Rapid discontinuation may increase the risk of seizures • If possible, taper dose over a period of 1–3 months Overdose: • Can be fatal, but patients have survived valproic acid levels as high as 2120 mg/L • Symptoms include: somnolence, heart block, coma • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes valproic acid from blood and, therefore, serves as a useful procedure in cases of overdose

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Tests and therapeutic drug monitoring: • Before starting: obtain complete blood count and transaminases • Inform all female patients of childbearing age about the teratogenicity (spina bifida) and the importance of avoiding an unplanned pregnancy • During treatment: blood count and liver function tests at the latest after 2 months, then at least every 6 months throughout treatment • Consider vitamin D level and dual energy x-ray absorptiometry (DEXA) bone scan in patients at risk for osteopenia • Monitor weight and BMI during treatment • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at valproic acid plasma concentrations of 50–100 mg/L (­350–700 μmol/L) –– The conversion factor from mg/L to μmol/L is 6.93 (i.e., 1 mg/L = 6.93 μmol/L) –– Because enteric coated valproic acid is a delayed release formulation, the lowest plasma level of a 24-hour period may not be before the morning dose, but rather in the late morning or early afternoon –– The reference range of valproic acid in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Valproic acid can be monitored by use of saliva, however, concentrations are not a good reflection of the free nonprotein bound plasma concentration and that is pharmacologically relevant • Before giving a drug that can cause weight gain to an overweight or obese patient, consider determining whether the patient already has pre-diabetes (fasting plasma glucose 100–125 mg/ dL), diabetes (fasting plasma glucose greater than 126 mg/dL), or dyslipidemia (increased total cholesterol, LDL cholesterol, and triglycerides; decreased HDL cholesterol), and treat or refer such patients for treatment, including nutrition and weight management, physical activity counseling, smoking cessation, and medical manage­­ment Other warnings/precautions: • Patients should be monitored carefully for signs of unusual bleeding or bruising • Obtain liver function tests in cases of symptoms suggestive of valproic acid hepatotoxicity, which include nausea, vomiting, anorexia, lethargy, jaundice, edema (predominantly facial), and at times of loss of seizure control • Obtain serum amylase and lipase in cases of symptoms suggestive of pancreatitis, which include vomiting, abdominal pain, nausea, and anorexia

the epilepsy prescriber’s guide to antiepileptic drugs • Somnolence may be more common in the elderly and may be associated with dehydration, reduced nutritional intake, and weight loss, requiring slower dosage increases, lower doses, and monitoring of fluid and nutritional intake • Evaluate for urea cycle disorders, as hyperammonemic encephalopathy, sometimes fatal, has been associated with valproate administration in these uncommon disorders; urea cycle disorders such as ornithine transcarbamylase deficiency, are associated with unexplained encephalopathy, mental retardation, elevated plasma ammonia, cyclical vomiting, and lethargy

Special populations

Do not use: • In patients with known urea cycle disorder (severe hyperammonemia) • In patients with hepatic disease or significant hepatic dysfunction • In patients with a history of pancreatitis • In patients with pre-existing thrombocytopenia • In patients with suspected mitochondrial disorder • Use with great caution in infants 2 years old or younger, especially in combination with other antiepileptic drugs • If there is a proven allergy to valproic acid, sodium valproate, or any excipients

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Special populations Renal impairment: • Renal disease has little or no impact on valproic acid pharmacokinetics, although protein binding may be reduced • Because valproic acid can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of valproic acid Hepatic impairment: • Valproic acid is extensively metabolized and consequently lower doses will be required in patients with hepatic impairment • Liver cirrhosis may lead to decreased protein binding and decreased clearance of valproic acid Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults • Risk of fatal hepatotoxicity is highest in infants 2 years of age and younger, especially in AED polytherapy • Use in children requires close medical supervision

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Elderly: • Elderly patients are more susceptible to adverse effects (especially somnolence) and, therefore, often do better at lower doses • Because of an age-related reduction in renal and hepatic function, lower valproate doses are appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities and, therefore, the risk of pharmacokinetic interactions with valproate is substantial • Because of a tendency for lower serum albumin values, elderly patients may have a higher free (unbound) fraction of valproic acid • Sedation in the elderly may be more common and associated with dehydration, reduced nutritional intake, and weight loss • Monitor fluid and nutritional intake Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Valproate is classified by the US Food and Drug Administration as risk category D [positive evidence of risk to human fetus; potential benefits may still justify its use during pregnancy] • When taken during pregnancy, valproic acid can cause major malformations, including neural tube defects, and possible developmental delay in offspring; this may be dose-related • Careful and early monitoring with fetal ultrasound • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • If possible, start on folate 1 mg/day early in pregnancy to reduce risk of neural tube defects • If drug is continued, consider vitamin K during the last 6 weeks of pregnancy to reduce risks of bleeding • Seizures, even mild seizures, may cause harm to the embryo/fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than valproic acid monotherapy • Taper drug if discontinuing • During pregnancy valproic acid pharmacokinetics change significantly so that valproic acid plasma concentrations decrease by 50% and free valproic acid plasma concentrations decrease by 29% due to increased clearance; binding is significantly decreased during pregnancy resulting in an increased free fraction of the drug particularly at higher plasma concentrations; an increase in valproate dose may be required in some patients

the epilepsy prescriber’s guide to antiepileptic drugs Breast feeding • Breast milk: 4–20% of maternal plasma levels • Breastfed infants: valproic acid plasma levels are 4–12% of maternal plasma levels • The potential benefit to the mother should be weighed against the potential risk to the infant when considering recommendations regarding nursing • If drug is continued while breast feeding, infant should be monitored for possible adverse effects, including hematological effects • If adverse effects are observed recommend bottle feed

Valproate, overall role

The overall place of valproate in the treatment of epilepsy Valproate is considered to be a broad spectrum antiepileptic drug, effective against all types of seizures and epilepsies. It is generally considered the first-line therapy for all types of generalized seizures (idiopathic and symptomatic, e.g., childhood and juvenile absence epilepsy, juvenile myoclonic epilepsy, benign myoclonic epilepsy in infants, myoclonic astatic epilepsy, epilepsy with myoclonic absences, eyelid myoclonus with absences), progressive myoclonic epilepsy, and photosensitive epilepsy. However, valproate is possibly slightly less effective than carbamazepine against partial seizures and is more efficacious than lamotrigine and better tolerated than topiramate in patients with generalized and unclassified epilepsies. Seizure aggravation is not a feature of valproate but when it occurs it is usually in a specific clinical context such as overdose, encephalopathy, or hepatic or metabolic disorders. The serious adverse effects, particularly in women of childbearing potential and in patients of early childhood should always be considered.

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Primary seizure types: • Juvenile myoclonic epilepsy (myoclonic, absence, and generalized tonic–clonic seizures) • Absence seizures • Myoclonic seizures • Cryptogenic or symptomatic generalized epilepsies • Lennox-Gastaut syndrome Secondary seizure types: • Partial seizures • Infantile spasms (West syndrome) Potential advantages: • Valproate has a broad spectrum of seizure protection • It is among the best or is the best antiepileptic drug for the treatment of idiopathic generalized epilepsies

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• No other antiepileptic drug has better efficacy than valproate in primarily generalized seizures although some of the new antiepileptic drugs (such as levetiracetam or lamotrigine) are better tolerated • Also potentially effective in the more therapy-resistant cryptogenic or symptomatic generalized epilepsies • Available in oral formulations of various strengths and as a parenteral formulation Potential disadvantages: • Idiosyncratic and other adverse effects, some potentially severe • Requires frequent blood testing and close monitoring • Pharmacokinetics are not linear due to saturable protein binding • Associated with significant pharmacokinetic interactions and usually acts as an inhibitor of hepatic metabolism • Potential teratogen, perhaps more substantive than any other antiepileptic drug

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Suggested reading Asconapé JJ, Penry JK, Dreifuss FE, Riela A, Mirza W. Valproateassociated pancreatitis. Epilepsia 1993; 34: 177–183. Biton V, Mirza W, Montouris G, Vuong A, Hammer AE, Barrett PS. Weight change associated with valproate and lamotrigine monotherapy in patients with epilepsy. Neurology 2001; 56:  172–177. Bryant AE, Dreifuss FE. Valproic acid hepatic fatalities. III. U.S. experience since 1986. Neurology 1996; 46: 465–469. Glaucer TA, Cnaan A, Shinnar S, Hirtz DG, Dlugos D, Masur D, Clark PO, Capparelli EV, Adamson PC. For the Childhood Absence Epilepsy Study Group. Ethosuximide, valproic acid, and lamotrigine in childhood absence epilepsy. New England Journal of Medicine 2010; 362: 790–799. Limdi NA, Shimpi AV, Faught E, Gomez CR, Burneo JG. Efficacy of rapid IV administration of valproic acid for status epilepticus. Neurology 2005; 64: 353–355. Marson AG, Williamson PR, Clough H, Hutton JL, Chadwick DW; Epilepsy Monotherapy Trial Group. Carbamazepine versus valproate monotherapy for epilepsy: a meta-analysis. Epilepsia 2002; 43: 505–513. Mattson RH, Cramer JA, Collins JF; Dept. of VA Epilepsy Cooperative Study No. 264 Group. A comparison of valproate with carbamazepine for the treatment of complex partial seizures and secondarily generalized tonic-clonic seizures in adults. New England Journal of Medicine 1992; 327: 765–771. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005.

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Patsalos PN, Berry DJ, Bourgeois BF, Cloyd JC, Glauser TA, Johannessen SI, Leppik IE, Tomson T, Perucca E. Antiepileptic drugs  – Best practice guidelines for therapeutic drug monitoring: a position paper by the Subcommission on Therapeutic Drug Monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia 2008; 49: 1239–1276. Ramsey RE, Wilder BJ, Murphy JV, Holmes GL, Uthman B. Efficacy and safety of valproic acid versus phenytoin as sole therapy for newly diagnosed primary generalized tonic-clonic seizures. Journal of Epilepsy 1992; 5: 55–60. Sommerville KS, Dutta S, Biton V, Zhang Y, Cloyd JC, Uthman B. Bioavailability of a divalproex extended-release formulation versus the conventional divalproex formulation in adult patients receiving enzyme-inducing antiepileptic drugs. Clinical Drug Investigation 2003; 23: 661–670. Villareal HJ, Wilder BJ, Willmore LJ, Bauman AW, Hammond EJ, Bruni J. Effect of valproic acid on spike and wave discharges in patients with absence seizures. Neurology 1978; 28: 886–891. Wyszynski DF, Nambisan M, Surve T, Alsdorf RM, Smith CR, Holmes LB. Antiepileptic drug pregnancy registry. Increased rate of major malformations in offspring exposed to valproate during pregnancy. Neurology 2005; 64: 961–965.

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Vigabatrin Therapeutics Chemical name and structure: Vigabatrin, (±)-amino-hex-5-enoic acid, is supplied as a racemic mixture of two enantiomers in equal proportions:  the (S+)enantiomer and the R(-)-enantiomer, with only the (S+)-enantiomer being pharmacologically active. It is a white to off-white crystalline solid, with a molecular weight of 129.2 and an empirical formula of C6H11NO2 . COOH

NH2

Vigabatrin

Brand names: • Sabril; Sabrilan; Sabrilex Generics available: • No Licensed indications for epilepsy: • Adjunctive treatment of partial seizures with and without secondary generalization not satisfactorily controlled with other antiepileptic drugs (UK-SPC) • Monotherapy for the management of infantile spasms (West syndrome) (UK-SPC) Licensed indications for non-epilepsy conditions: • There are none Nonlicensed use for epilepsy: • There are none Nonlicensed use for non-epilepsy conditions: • There are none

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Ineffective (contraindicated): • Aggravates typical absence seizures and provokes absence status epilepticus • Idiopathic generalized epilepsies with absences • May exaggerate atypical absences such as those occurring in LennoxGastaut syndrome • May exaggerate myoclonic seizures such as those occurring in progressive and nonprogressive myoclonic epilepsies

the epilepsy prescriber’s guide to antiepileptic drugs Mechanism of action: • As an analog of GABA, it was specifically developed to increase brain GABA • Binds irreversibly and covalently to GABA-transaminase causing permanent inactivation • Inactivation of GABA-transaminase, which is responsible for the breakdown of GABA in neurons and glia, results in an increase in brain (synaptic) GABA

Pharmacokinetics Absorption and distribution: • Oral bioavailability: 60–80% • Food co-ingestion:  neither delays the rate of absorption nor decreases the extent of absorption • Tmax: 1–2 hours • Time to steady state: 1–2 days • Pharmacokinetics: linear • Protein binding: 0% • Volume of distribution: 0.8 L/kg • Salivary concentrations:  vigabatrin is secreted into saliva but it is not known whether such concentrations are similar to the unbound levels seen in plasma

Drug interaction profile

Efficacy profile: • The goal of treatment is complete remission of seizures • Efficacy should be apparent within 3 months of treatment initiation • Discontinuation should occur in the absence of definitive, meaningful seizure reduction during this period to eliminate the potential for developing peripheral visual field defects

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Metabolism: • Vigabatrin is not metabolized Elimination: • Following a single dose, half-life values in adults are 5–8 hours • The renal clearance of vigabatrin is proportional to the creatinine clearance • Renal excretion:  ~100% of an administered dose is excreted unchanged in urine

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on vigabatrin: –– To date, there have been no reports of AEDs affecting the clearance of vigabatrin and affecting vigabatrin plasma levels

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• Interactions between AEDs: effects by vigabatrin: –– Vigabatrin can decrease plasma levels of phenytoin • Interactions between AEDs and non-AED drugs:  effects on vigabatrin: –– To date, there have been no reports of other non-AED drugs affecting the clearance of vigabatrin and affecting vigabatrin plasma levels • Interactions between AEDs and non-AED drugs:  effects by vigabatrin: –– To date, there have been no reports of vigabatrin affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • To date, none have been reported

Vigabatrin

Hormonal contraception: • Vigabatrin does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

Adverse effects How drug causes adverse effects: • It is possible that the peripheral visual field defects associated with vigabatrin are the consequence of specific accumulation of vigabatrin in the retina • The visual field defects may be the consequence of an idiosyncratic adverse drug reaction, although dose- and duration-dependent toxicity have also been documented Common adverse effects: • Visual field defects (males have a two-fold greater risk than females), diplopia, nystagmus • Sedation, dizziness, headache, ataxia • Memory, cognitive, mental (thought disturbances) and behavioral disturbances (e.g., excitation and agitation especially in children) • Psychosis, mania, depression • Paresthesia • Nausea, abdominal pain • Fatigue

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Life-threatening or dangerous adverse effects: • May experience an increase in seizure frequency, including status epilepticus – patients with myoclonic or absence seizures may be particularly at risk of status epilepticus • Rare encephalopathic symptoms such as marked sedation, stupor and confusion

the epilepsy prescriber’s guide to antiepileptic drugs Rare and not life-threatening adverse effects: • Angioedema • Urticaria • Hallucinations • Rash • Retinal atrophy, optic neuritis

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Weight change: • Weight gain is common

Dosing and use Usual dosage range: • Adults: 1000–3000 mg/day • Children: 2000–3000 mg/day • Infants (monotherapy for infantile spasms): 150–200 mg/kg/day

Dosing and use

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician • Visual field defects, which usually present at 6 months–2 years, are not usually reversible, therefore, if the patient is not responding to treatment (within 3 months) vigabatrin should be withdrawn

Available formulations: • Tablets: 500 mg • Sachet: 500 mg (sugar-free powder) How to dose: • When initiating vigabatrin treatment start with a low dose and titrate slowly so as to minimize adverse effects –– For adults: start treatment with 500 mg/day; each week increase by 500 mg/day; maintenance dose generally 1000–3000 mg/day given either as a single dose or in two equally divided doses –– Children:  start treatment with 40 mg/kg/day in one or two divided doses and increase at weekly intervals depending on body weight; maintenance dose of 500–1000 mg/kg/day, ­1000–1500 mg/kg/day, 1500–3000 mg/kg/day and 2000–3000 mg/kg/day for infants weighing 10–15 kg, 15–30 kg, 30–50 kg, and >50 kg, respectively, is often required –– Infants (monotherapy for infantile spasms):  start treatment with 50 mg/kg/day and titrate according to response over 7 days to a maximum of 150–200 mg/kg/day given as a single dose or in divided doses; maintenance dose generally 150–200 mg/kg/day Dosing tips: • The powder (sachet) formulation can be added to water, fruit juice, or milk and ingested immediately as a solution

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• If the patient does not respond within 3 months of initiation of treatment, vigabatrin should be withdrawn so as to avoid induction of visual field defects which occurs in 30% of patients • Adverse effects in adults, such as sedation, drowsiness, fatigue, and impaired concentration, and in children, such as excitation and agitation, generally present at the beginning of treatment and decrease with time How to withdraw drug: • May need to adjust dosage of concurrent phenytoin medication as vigabatrin is being discontinued, because plasma levels of phenytoin may change (see Pharmacokinetic drug interactions section) • Taper: a gradual dose reduction over a 2- to 4-week period should be undertaken • Rapid discontinuation may increase the risk of rebound seizures

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Overdose: • To date, no fatalities have been reported • Most common overdoses range from 7.5–30 g, however, ingestions up to 90 g have been reported • Most common symptoms include: drowsiness and coma • Other less frequently reported symptoms include: vertigo, headache, psychosis, respiratory depression or apnea, bradycardia, hypotension, agitation, irritability, confusion, abnormal behavior, and speech disorder • If indicated the stomach should be emptied by lavage or by induction of emesis • Hemodialysis removes 40–60% of vigabatrin from blood and, therefore, serves as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Before starting: blood count, liver, and kidney function tests • Before starting: all patients should have ophthalmological consultation with visual field examination using static perimetry • During treatment:  blood count, liver and kidney function tests every 6–12 months • During treatment:  systematic perimetry (for adults) or visualevoked potentials (for children aged < 9 years) every 6 months; electroretinography may be useful but should only be used in adults who are unable to co-operate with perimetry, or the very young • Therapeutic drug monitoring: –– At doses between 1000 and 3000 mg/day, the expected trough vigabatrin plasma concentrations are in the range of 0.8–36 mg/L (6–279 μmol/L) –– The conversion factor from mg/L to μmol/L is 7.74 (i.e., 1 mg/L = 7.74 μmol/L)

the epilepsy prescriber’s guide to antiepileptic drugs

Other warnings/precautions: • Because visual field defects are irreversible even after discontinuation of vigabatrin, vigabatrin should only be prescribed after a careful assessment of the balance of benefits and risks compared with alternative treatments • The usual pattern of visual field defects entails a concentric constriction of the visual field of both eyes, which is generally more marked nasally than temporally; in the central visual field (within 30 degrees of eccentricity) an annular nasal defect is frequently seen but central visual acuity is not impaired – however, the visual field defects reported in patients receiving vigabatrin have ranged from mild to severe with the latter potentially disabling • Should not be used concomitantly with other retinotoxic drugs • Use with caution in patients with a history of psychosis, depression, or behavioral problems • Many patients may experience reductions in their alanine transferase and aspartate transferase activities, which is considered to be the result of vigabatrin, and is usually asymptomatic; reductions in hemoglobin concentrations can also occur and may on occasion attain clinical significance

V

Dosing and use

–– Overall, the rationale for monitoring does not apply to vigabatrin because there is no correlation between plasma concentrations and clinical efficacy, and the duration of vigabatrin’s action long outlasts its plasma half-life. This is attributable to the mechanism of action of vigabatrin whereby the destruction of the enzyme GABA-transaminase occurs and the duration of the effect of the drug is dependent on the rate of GABAtransaminase r­ e-synthesis, which requires many days –– Measurement of plasma vigabatrin concentrations may be useful as a check on recent compliance –– The reference range of vigabatrin in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– There are no data indicating the usefulness of monitoring vigabatrin by use of saliva • Before giving a drug that can cause weight gain to an overweight or obese patient, consider determining whether the patient already has prediabetes (fasting plasma glucose 100–125 mg/ dl), diabetes (fasting plasma glucose greater than 126 mg/dl), or dyslipidemia (increased total cholesterol, LDL cholesterol and triglycerides; decreased HDL cholesterol), and treat or refer such patients for treatment, including nutrition and weight management, physical activity counseling, smoking cessation, and medical management • Monitor weight and BMI during treatment

293

the epilepsy prescriber’s guide to antiepileptic drugs

V

Do not use: • If patient has any pre-existing clinically significant visual field defect • If patient has a proven allergy to vigabatrin or to any excipient

Special populations Renal impairment: • Vigabatrin is renally excreted, so the dose may need to be ­lowered – particularly in patients with a CrCL of <60 mL/min • Because vigabatrin can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of vigabatrin Hepatic impairment: • Vigabatrin is not metabolized in the liver and consequently dose adjustment will not be necessary

Vigabatrin

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults – specific dosing recommendations are in place for children Elderly: • Elderly patients are more susceptible to adverse effects and, therefore, tolerate lower doses better • Because of an age-related reduction in renal function, lower vigabatrin doses are appropriate and patients should be monitored for undesirable effects such as sedation and confusion • Invariably the elderly are prescribed drug therapies for concurrent comorbidities, but the risk of pharmacokinetic interactions with vigabatrin is low or nonexistent

294

Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Vigabatrin is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus

the epilepsy prescriber’s guide to antiepileptic drugs • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than vigabatrin monotherapy • Taper drug if discontinuing • Seizures, even mild seizures, may cause harm to the embryo/fetus • There are no available data on the pharmacokinetic changes of vigabatrin during pregnancy

The overall place of vigabatrin in the treatment of epilepsy Vigabatrin is particularly effective for the treatment of infantile spasms (West syndrome), particularly in patients with cryptogenic etiology, tuberous sclerosis, or localized cortical dysplasia. It is also effective in simple partial and complex partial seizures with or without secondary generalization. Because spasm cessation can occur within 2 weeks following initiation of vigabatrin treatment and because of the desirability of rapid seizure control to reduce secondary psychomotor regression or transition to other catastrophic seizure types (e.g., Lennox-Gastaut syndrome), vigabatrin is becoming the drug of choice for the management of infantile spasms. Furthermore, given the catastrophic nature of infantile spasms, the risk of peripheral visual field defects may be acceptable if appropriate seizure control can be achieved, thus providing an improved opportunity for normal development.

Vigabatrin, overall role

Breast feeding • Breast milk: 4–20% of maternal plasma levels • Breastfed infants: it is not known what plasma vigabatrin concentrations are achieved in breastfed infants compared with the levels of their mothers • If drug is continued while breast feeding, infant should be monitored for possible adverse effects • If adverse effects are observed recommend bottle feed

V

Primary seizure types: • Simple partial or complex partial epilepsy with or without secondary generalization • Infantile spasms (West syndrome) Secondary seizure types: • None Potential advantages: • Vigabatrin is an effective antiepileptic drug for the treatment of focal epilepsies of any type (idiopathic or symptomatic) with or without secondarily generalized tonic–clonic seizures

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V

• Although corticotrophin/corticosteroids are efficacious in 50–75% of patients with infantile spasms, relapse rates are high and adverse effects are substantial • Because it is excreted exclusively by renal elimination, vigabatrin is not associated with any significant pharmacokinetic interactions Potential disadvantages: • Visual field defects which require frequent monitoring • Potential teratogen, but not more than most other antiepileptic drugs

Vigabatrin 296

Suggested reading Conway M, Cubbidge RP, Hoskings SL. Visual field severity indices demonstrate dose-dependent visual loss from vigabatrin therapy. Epilepsia 2008; 49: 108–116. Johannessen Landmark C, Patsalos PN. Drug interactions involving the new second- and third-generation antiepileptic drugs. Expert Reviews in Neurotherapeutics 2010; 10: 119–140. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Patsalos PN, Duncan JS. The pharmacology and pharmacokinetics of vigabatrin. Reviews in Contemporary Pharmacotherapy 1995; 6: 447–456. Ryan MF, Samy A, Young J. Vigabatrin causes profound reduction in serum alanine transferase activity. Annals of Clinical Biochemistry 1996; 33: 257–258. Shields WD. Infantile spasms:  little seizures, big consequences. Epilepsy Currents 2006; 6: 63–69. Sills GJ, Patsalos PN, Butler E, Forrest G, Ratnaraj N, Brodie MJ. Visual field constrictions. Accumulation of vigabatrin but not tiagabine in the retina. Neurology 2001; 57: 196–200. Wheles JW, Clarke DF, Arzimanoglou A, Carpenter D. Treatment of pediatric epilepsy: European expert opinion, 2007. Epileptic Disorders 2007; 9: 353–412. Wheles JW, Ramsey RE, Collins SD. Vigabatrin. Neurotherapeutics 2007; 4: 163–172. Willmore LJ, Abelson MB, Ben-Menachem E, Pellock JM, Shields WD. Vigabatrin: 2008 update. Epilepsia 2009; 50: 163–173.

the epilepsy prescriber’s guide to antiepileptic drugs

Zonisamide Therapeutics Chemical name and structure: Zonisamide, 1,2-benzisoxazole-3-methanesulfonamide, is a white to pale yellow crystalline powder, with a molecular weight of 212.23 and an empirical formula of C 8H8N2O3S.

Z

O N CH2SO2NH2

Generics available: • Yes

therapeutics

Brand names: • Excegran • Zonegran

Licensed indications for epilepsy: • Adjunctive therapy for partial and secondarily generalized seizures in adults (UK-SPC; FDA-PI) Licensed indications for non-epilepsy conditions: • Parkinson disease (licensed in Japan) Nonlicensed use for epilepsy: • Absence seizures • Infantile spasms (West syndrome) • Juvenile myoclonic epilepsy • Lennox-Gastaut syndrome • Myoclonic astatic epilepsy (Doose syndrome) • Myoclonic seizures • Progressive myoclonus epilepsy (Unverricht-Lundborg and Lafora disease) Nonlicensed use for non-epilepsy conditions: • Binge-eating disorder • Bipolar disorder • Migraine • Neuropathic pain • Psychotropic drug-induced weight gain

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the epilepsy prescriber’s guide to antiepileptic drugs

Z

Ineffective (contraindicated): • Zonisamide is potentially effective against all seizure types and is not contraindicated for any seizure type or epilepsy • There is no evidence to support its use for benign rolandic epilepsy or for the prophylaxis of febrile seizures • Zonisamide does not commonly exacerbate seizures Mechanism of action: • Partial blockade of activity-dependent sodium channels • Blockade of the T-type calcium channels • Inhibition of potassium-mediated glutamate release • Increase in extracellular levels of dopamine and serotonin • Up-regulation of excitatory amino-acid carrier-1 (EAAC-1) • Down-regulation of the expression of GABA transporter-1 (GAT-1) • Carbonic anhydrase inhibition, but potency is much lower than that of acetazolamide

Zonisamide

Efficacy profile: • The goal of treatment is complete remission of seizures • Therapeutic effect usually evident within 2–4 weeks • Once chronic therapy is initiated, it is usually continued for at least 2 years following the last seizure • No unusual incidence of loss of efficacy • If zonisamide is ineffective or only partially effective, it can be replaced by or combined with another antiepileptic drug that is appropriate for the patient’s seizure type or epilepsy syndrome

Pharmacokinetics Absorption and distribution: • Oral bioavailability: >90% • Food co-ingestion: delays the rate of absorption (Tmax, 4–6 hours) but does not decrease the extent of absorption • Tmax: 2–5 hours • Time to steady state: 10–15 days • Pharmacokinetics: linear • Protein binding: ~40% • Volume of distribution: 1.0–1.9 L/kg • Salivary concentrations:  zonisamide is secreted into saliva and concentrations are similar to the unbound levels seen in plasma

298

Metabolism: • Zonisamide undergoes acetylation to form N-acetyl zonisamide and reduction to form 2-sulfamoylacetylphenol – the latter being subsequently glucuronidated

the epilepsy prescriber’s guide to antiepileptic drugs • The reduction of zonisamide to 2-sulfamoylacetylphenol is mediated by the CYP3A4 isoenzyme • Metabolites are not pharmacologically active • Autoinduction is not a feature of zonisamide metabolism

Drug interaction profile

Elimination: • In the absence of enzyme-inducing AEDs, half-life values for zonisamide are 50–70 hours • In the presence of enzyme-inducing AEDs, half-life values for zonisamide are 25–35 hours • No data are available regarding the elimination half-life of zonisamide in children • Renal excretion:  ~65% of an administered dose is excreted as metabolites in urine; 50% as the 2-sulfamoylacetylphenol glucuronide and 15% as N-acetyl zonisamide • Renal excretion:  ~35% of an administered dose is excreted as unchanged zonisamide in urine

Z

Drug interaction profile Pharmacokinetic drug interactions: • Interactions between AEDs: effects on zonisamide: –– Carbamazepine, phenobarbital, phenytoin, primidone, and valproic acid can increase the clearance of zonisamide and decrease zonisamide plasma levels • Interactions between AEDs: effects by zonisamide: –– To date, there have been no reports of zonisamide affecting the clearance of other AEDs and affecting their plasma levels • Interactions between AEDs and non-AED drugs:  effects on zonisamide: –– Risperidone can decrease zonisamide plasma levels • Interactions between AEDs and non-AED drugs:  effects by zonisamide: –– To date, there have been no reports of zonisamide affecting the clearance of other non-AED drugs and affecting their plasma levels Pharmacodynamic drug interactions: • To date, none have been reported Hormonal contraception: • Zonisamide does not enhance the metabolism of oral contraceptives so as to decrease plasma levels of hormonal contraceptives and, therefore, does not compromise contraception control

299

the epilepsy prescriber’s guide to antiepileptic drugs

Z

Adverse effects How drug causes adverse effects: • Mechanism by which zonisamide causes adverse effects has not been established • Carbonic anhydrase inhibition by zonisamide, although not or only minimally involved in its antiepileptic activity, may be the mechanism responsible for some of the clinical adverse effects, such as metabolic acidosis, paresthesias, kidney stones and hypohydrosis

Zonisamide

Common adverse effects: Unlike sulfonamide antibiotic compounds, zonisamide does not contain an arylamine group at the N4-position, which contributes to allergic reactions to sulfonamide antibiotics • Drowsiness, fatigue • Ataxia • Decrease in spontaneity • Psychomotor slowing • Impairments in verbal learning (may be transient) • Behavioral or psychiatric adverse effects (e.g., aggression, agitation, irritability, poor attention, hallucinations, hyperactivity, dysphoria, paranoia, and psychosis) • Anorexia, nausea, abdominal pain, vomiting and weight loss • Metabolic acidosis (lowered serum bicarbonate or CO2 , especially in children) • Hypohydrosis (decreased sweating, especially in children, may lead to hyperthermia) • Allergic rash (risk lower than for antibiotic sulfonamides) Life-threatening or dangerous adverse effects: • Very rarely Stevens-Johnson syndrome, toxic epidermic necrolysis, hepatic necrosis • Rare blood dyscrasias (aplastic anemia, agranulocytosis) • Rare oligohydrosis and hyperthermia (pediatric patients) • Sudden unexplained deaths have occurred (unknown if related to zonisamide use) Rare and not life-threatening adverse effects: • Nephrolithiasis (1–2%) • Paresthesias, mostly tingling in the fingers and toes • Mild elevation of serum creatinine and blood urea nitrogen values Weight change: • Weight loss is common

300

What to do about adverse effects: • Discuss common and severe adverse effects with patients or parents before starting medication, including symptoms that should be reported to the physician

the epilepsy prescriber’s guide to antiepileptic drugs

Dosing and use Usual dosage range: • Adults:  100–600 mg/day (the lower doses may be sufficient in monotherapy and the higher doses may be necessary with enzymeinducing AEDs) • Children: 8 mg/kg/day (monotherapy); 12 mg/kg/day (with enzyme-inducing AEDs)

Z

Dosing and use

• Discuss symptoms associated with kidney stones, glaucoma, and hypohydrosis • Some CNS-related adverse effects may be lessened by slow titration, but they may persist at low doses despite slow titration • Metabolic acidosis is usually compensated, but patients may be treated with oral bicarbonate for CO2 values of 15–18 mEq/L or less • If possible, zonisamide should not be administered to patients on acetazolamide, sulthiame, topiramate, or on the ketogenic diet, because these treatments also predispose to metabolic acidosis and to kidney stones • Patients should be encouraged to drink liberally while on zonisamide to reduce risk of kidney stones • Anorexia and weight loss may improve with dosage reduction • Children who benefit from zonisamide treatment but experience hypohydrosis may experience improved heat tolerance after being sponged down or wrapped in a wet towel • Cognitive and behavioral adverse effects often improve following reduction of the dose of zonisamide

Available formulations: • Capsules: 25 mg, 50 mg, 100 mg How to dose: –– For adults and children over 12 years of age: start treatment with 100 mg/day, once or twice daily; at intervals of 2 weeks increase as needed and as tolerated by 100 mg/day; maintenance dose generally 100–600 mg/day –– Children: start treatment with 1.0–2.0 mg/kg/day, once or twice daily; at intervals of 2 weeks increase as needed and as tolerated by 1.0–2.0 mg/kg/day; maintenance dose generally 8–12 mg/kg/ day; doses of 20 mg/kg/day may be necessary and well tolerated, especially in infants; dosage requirements may increase two-fold in children co-prescribed enzyme-inducing AEDs Dosing tips: • Slow dose titration may delay onset of therapeutic action but enhance tolerability to sedating effects

301

the epilepsy prescriber’s guide to antiepileptic drugs

Z

Zonisamide 302

• For intolerable sedation, can give most of the dose at night and less during the day • Adverse effects may increase notably at doses greater than 300 mg/day • Some patients may do very well at relatively low doses of zonisamide, such as 200 mg/day in adults or 4–6 mg/kg/day in children; the response to treatment should be assessed at these doses before increasing the dose further • In view of the long elimination half-life, zonisamide can be administered once or twice daily How to withdraw drug: • There is no need to adjust dosage of concurrent medications as zonisamide is being discontinued, because plasma levels of other drugs do not change (see Pharmacokinetic drug interactions section) • No data are available on potential for withdrawal seizures or symptoms upon rapid discontinuation • Rapid discontinuation may increase the risk of seizures, however, if possible, taper dose over a period of 1–3 months Overdose: • No fatalities have been reported to date • A patient who ingested an overdose of zonisamide and had a serum level of 100.1 mg/L (471.5 μmol/L) after 31 hours developed coma, bradycardia, hypotension and respiratory depression; the outcome was good following supportive care • Severe metabolic acidosis could develop • The stomach should be emptied immediately by lavage or by induction of emesis • Hemodialysis removes zonisamide from blood and, therefore, serves as a useful procedure in cases of overdose Tests and therapeutic drug monitoring: • Serum bicarbonate (CO2) should be measured before treatment and then periodically • Other routine laboratory testing is not necessary • Consider periodic monitoring of blood urea nitrogen and creatinine • Therapeutic drug monitoring: –– Optimum seizure control in patients on monotherapy is most likely to occur at zonisamide plasma concentrations of 10–40 mg/L (47–188 μmol/L) –– The conversion factor from mg/L to μmol/L is 4.71 (i.e., 1 mg/L = 4.71 μmol/L) –– Drowsiness is more likely to occur at levels >40 mg/L (> 188 μmol/L) –– Because zonisamide has a high binding affinity to the intracellular compartment of erythrocytes, this may lead to a false elevation of the plasma zonisamide level in hemolyzed blood samples

the epilepsy prescriber’s guide to antiepileptic drugs –– The reference range of zonisamide in plasma is considered to be the same for children and adults although no data are available to support this clinical practice –– Zonisamide can be monitored by use of saliva which is a measure of the free nonprotein bound plasma concentration and that is pharmacologically relevant

special populations

Other warnings/precautions: • Patients should be monitored carefully for evidence of cognitive adverse effects • Patients should be monitored carefully for evidence of kidney stones • Depressive effects may be increased by other CNS depressants (alcohol, MAOIs, other antiepileptic drugs) • Use with caution when combining with other drugs that predispose patients to heat-related disorders, including carbonic anhydrase inhibitors and anticholinergics • Life-threatening rashes have developed in association with zonisamide use; zonisamide should generally be discontinued at the first sign of serious rash • Patient should be instructed to report any symptoms of hypersensitivity immediately (fever; flu-like symptoms; rash; blisters on skin or in eyes, mouth, ears, nose, or genital areas; swelling of eyelids, conjunctivitis, lymphadenopathy) • Patients should be monitored for signs of unusual bleeding or bruising, mouth sores, infections, fever, and sore throat, as there may be an increased risk of aplastic anemia and agranulocytosis with zonisamide

Z

Do not use: • If patient has a proven allergy to zonisamide or to any of the excipients • Use with caution in patients undergoing treatments that are associated with an increase in risk of kidney stones, such as acetazolamide, sulthiame, topiramate, and the ketogenic diet • Use with caution in patients with a history of allergic rash to another medication • A history of allergic reaction to an antibiotic sulfonamide does not appear to be an absolute contraindication for the use of zonisamide, because there seems to be no specific allergic cross-­reactivity between antibiotic sulfonamides and all other sulfonamides

Special populations Renal impairment: • Zonisamide is renally excreted (35%), therefore, the dose may need to be lowered • At a CrCL of <20 mL/min, the clearance of zonisamide is reduced by 35%

303

the epilepsy prescriber’s guide to antiepileptic drugs

Z

• Because zonisamide can be removed by hemodialysis, patients receiving hemodialysis may require supplemental doses of zonisamide Hepatic impairment: • Zonisamide is substantially metabolized (65%) and consequently lower doses may be required • No studies on the effect of hepatic failure on the pharmacokinetics of zonisamide have been reported

Zonisamide 304

Children: • Children have an increased metabolic capacity and consequently higher doses on a mg/kg/day basis are usually required to achieve the equivalent therapeutic plasma levels seen in adults • Pharmacokinetic interactions in children are usually of a greater magnitude than that seen in adults • Children are at higher risk of developing metabolic acidosis as well as symptoms related to hypohydrosis Elderly: • The pharmacokinetics of zonisamide in elderly patients do not differ from those in adults • Elderly patients are more susceptible to adverse effects and, therefore, often do better at lower doses • Because of an age-related reduction in renal and hepatic function, lower zonisamide doses may be appropriate • Invariably the elderly are prescribed drug therapies for concurrent comorbidities; however the risk of pharmacokinetic interactions with zonisamide is minimal Pregnancy: • Specialist advice should be given to women who are of childbearing potential; they should be informed about the teratogenicity of all antiepileptic drugs and the importance of avoiding an unplanned pregnancy; the antiepileptic drug treatment regimen should be reviewed when a woman is planning to become pregnant • Rapid discontinuation of antiepileptic drugs should be avoided as this may lead to breakthrough seizures, which could have serious consequences for the woman and the unborn child • Zonisamide is classified by the US Food and Drug Administration as risk category C [some animal studies show adverse effects, no controlled studies in humans] • Use in women of childbearing potential requires weighing potential benefits to the mother against the risks to the fetus • Seizures, even mild seizures, may cause harm to the embryo/fetus • Use with other antiepileptic drugs in combination may cause a higher prevalence of teratogenic effects than zonisamide monotherapy • Taper drug if discontinuing

the epilepsy prescriber’s guide to antiepileptic drugs • Data on the pharmacokinetic changes of zonisamide during pregnancy are not available

The overall place of zonisamide in the treatment of epilepsy Zonisamide appears to be an effective broad spectrum antiepileptic drug. It is efficacious in partial seizures with or without generalized tonic–clonic seizures, primary and secondarily generalized seizures including epileptic spasms of West syndrome, other epileptic encephalopathies such as Ohtahara syndrome, and progressive and probably other myoclonic epilepsies such as Unverricht syndrome. At present zonisamide is considered second line therapy for partial seizures, is the drug of choice in progressive myoclonic epilepsy and is the drug of second choice for idiopathic generalized epilepsies with generalized tonic–clonic seizures, juvenile myoclonic epilepsy or the Lennox-Gastaut syndrome.

Zonisamide, overall role

Breast feeding • Breast milk: 90% of maternal plasma levels • Breastfed infants: zonisamide plasma levels are ~100% of maternal plasma levels • The potential benefit to the mother should be weighed against the potential risk to the infant when considering recommendations regarding nursing • If drug is continued while breast feeding, infant should be monitored for possible adverse effects, including sedation and irritation • If adverse effects are observed recommend bottle feed

Z

Primary seizure types: • Partial epilepsies • Progressive myoclonic epilepsy Secondary seizure types: • Myoclonic seizures • Idiopathic generalized epilepsies with generalized tonic–clonic seizures • Juvenile myoclonic epilepsy • Lennox-Gastaut syndrome • Myoclonic astatic epilepsy (Doose syndrome) • Infantile spasms (West syndrome) Potential advantages: • Broad spectrum of seizure protection • Zonisamide causes no pharmacokinetic interactions • Does not exacerbate seizures

305

the epilepsy prescriber’s guide to antiepileptic drugs

Z

Zonisamide 306

Potential disadvantages: • In contrast to topiramate, zonisamide can cause an allergic rash • Hypohydrosis can cause hyperthermia in children • Cognitive and psychotic episodes may be problematic • Nephrolithiasis is a concern • Potential teratogen, but not more than most other antiepileptic drugs

Suggested reading Brackett CC, Singh H, Block JH. Likelihood and mechanisms of cross-allergenicity between sulfonamide antibiotics and other drugs containing a sulfonamide functional group. Pharmacotherapy 2004; 24: 856–870. Brodie MJ, Duncan R, Vespignani H, Solyom A, Bitenskyy V, Lucas C. Dose-dependent safety and efficacy of zonisamide:  a ran­domized, double-blind, placebo-controlled study in patients with refractory partial seizures. Epilepsia 2005; 46: 31–41. Faught E, Ayala R, Montouris GG, Leppik IE. Randomized controlled trial of zonisamide for the treatment of refractory partialonset seizures. Neurology 2001; 57: 1774–1779. Glauser TA, Pellock JM. Zonisamide in pediatric epilepsy: review of the Japanese literature. Journal of Child Neurology 2002; 17: 87–96. Kim HL, Aldridge J, Rho JM. Clinical experience with zonisamide monotherapy and adjunctive therapy in children with epilepsy at a tertiary care referral center. Journal of Child Neurology 2005; 20: 212–219. Kyllerman M, Ben-Menachem E. Zonisamide for progressive myoclonus epilepsy: long-term observations in seven patients. Epilepsy Research 1998; 29: 109–114. Leppik IE. Practical prescribing and long-term efficacy and safety of zonisamide. Epilepsy Research 2006; 68S; S17-S24. Low PA, James S, Peschel T, Leong R, Rothstein A. Zonisamide and associated oligohydrosis and hyperthermia. Epilepsy Research 2004; 62: 27–34. Mimaki T. Clinical pharmacology and therapeutic drug monitoring of zonisamide. Therapeutic Drug Monitoring 1998; 29: 593–597. Patsalos PN. Anti-epileptic drug interactions. A clinical guide. Clarius Press: Guildford, UK; 2005. Suzuki Y, Imai K, Toribe Y, Ueda H, Yanagihara K, Shimono K, Okinaga T, Ono J, Nagai T, Matsuoka T, Tagawa T, Abe J, Morita Y, Fujikawa Y, Arai H, Mano T, Okada S. Long-term response to zonisamide in patients with West syndrome. Neurology 2002; 58: 1556–1559. Suzuki Y, Nagai T, Ono J, Imai K, Otani K, Tagawa T, Abe J, Shiomi M, Okada S. Zonisamide monotherapy in newly diagnosed infantile spasms. Epilepsia 1997; 38: 1035–1038.

Abbreviations

FDA-PI GABA GAT 1 HDL iv im LDL MAOIs NMDA PEMA PPD REM Tmax UK-BNF UGT UK-SPC

adrenocorticotropic hormone antiepileptic drug area under the concentration versus time curve body mass index blood urea nitrogen complete blood count central nervous system creatinine clearance cytochrome P450 excitatory amino-acid carrier-1 electrocardiogram dual energy x-ray absorptiometry electroencephalogram European Medicines Agency-Summary of Product Characteristics Food and Drug Administration-Product Information gamma-aminobutyric acid GABA transporter 1 high density lipoprotein intravenous intramuscular low density lipoprotein monoamine oxidase inhibitors N-methyl-D-aspartate phenyl-ethyl-malonamide purified protein derivative random eye movement time to maximum concentration United Kingdom-British National Formulary uridine glucuronyl transferase United Kingdom-Summary of Product Characteristics

abbreviations

ACTH AED AUC BMI BUN CBC CNS CrCl CYP EAAC-1 ECG DEXA EEG EMEA-SPC

307

the epilepsy prescriber’s guide to antiepileptic drugs Table: Interactions between new antiepileptic drugs (AEDs): Expected changes AED regimen. PRECBZ EXISTING AED

CLB

ESL

FBM

GBP LCM LTG

LEV OXC

AED Added ↔

↔

LTG⇓ ↔

?

NA

NA

?

?

NA

NA

LTG↓ NA

?

?

–

NA

NA

↔

NA

↔

CBZ

AI

CLB⇓ ESL↓ FBM⇓ DMCLB⇑

CLB

?

–

?

ESL

?

?

–

FBM

CBZ↓

CLB⇓

↔

H- OXC↓ ↔

CBZ-E↑ DMCLB⇑

abbreviations 

GBP

↔

NA

NA

FBM↑

–

NA

NA

↔

NA

LCM

↔

NA

NA

NA

NA

–

↔

↔

↔

LTG

↔

↔

?

NA

NA

↔

–

↔

NA

LEV

↔

↔

NA

NA

↔

↔

↔

–

NA

OXC

CBZ↓

?

?

?

NA

↔

LTG↓ NA

–

PB

CBZ⇓

? CLB⇓ DMCLB⇑

FBM⇓

↔

NA

LTG⇓ ↔

H- OXC↓

PHT

CBZ⇓

CLB⇓ ESL↓ FBM⇓ DMCLB⇑

↔

↔

LTG⇓ ↔

H- OXC↓

PGB

↔

NA

?

NA

?

NA

↔

PRM

CBZ⇓

CLB⇓

?

FBM⇓

↔

NA

LTG⇓ ↔

↔

?

RFN

CBZ↓

?

?

?

NA

NA

LTG↓ NA

?

STP

CBZ⇑

? CLB⇑ DMCLB⇑

?

NA

NA

?

NA

?

TGB

↔

NA

?

NA

NA

NA

NA

NA

↔

TPM

↔

?

?

?

NA

↔

↔

NA

?

VPA

CBZ-E⇑ ?

?

FBM↑

↔

↔

LTG⇑ ↔

↔

VGB

↔

NA

↔

NA

NA

NA

NA

NA

ZNS

CBZ↑↓ ?

?

?

NA

NA

↔

NA

?

NA

DMCLB⇑

NA

CBZ = carbamazepine; CBZ-E = carbamazepine-10,11-epoxide (active metabolite of CBZ); CLB = FBM = felbamate; GBP = gabapentin; H-OXC = 10-hydroxy-oxcarbazepine (active metabolite of PB = phenobarbital; PHT = phenytoin; PGB = pregabalin; PRM = primidone; RFN = rufinamide; ZNS = zonisamide. AI = autoinduction; NA = none anticipated; NCCP = not commonly co-prescribed; ↔ = No change; ⇓ = a usually clinically significant decrease in plasma level; ↑ = a usually minor (or inconsistent)

308

the epilepsy prescriber’s guide to antiepileptic drugs in plasma concentrations (levels) when an AED is added to a pre-existing PB

PHT

PGB PRM

RFN

STP

TGB TPM

VPA

VGB

↔

PHT↑↓ ↔

?

PHT↑

NA

PRM↑ ?

?

?

?

?

PHT↑

NA

?

?

?

?

TPM↓ ?

PB⇑

PHT⇑

NA

?

?

?

?

?

VPA⇑ ↔

?

↔

↔

?

NA

NA

NA

NA

↔

↔

NA

NA

NA

↔

NA

NA

NA

NA

NA

↔

↔

NA

NA

↔

↔

↔

↔

↔

?

NA

↔

VPA↓ NA

↔

↔

↔

↔

↔

NA

NA

NA

NA

↔

NA

NA

PB↑

PHT↑

NA

?

?

?

?

TPM↓ ↔

NA

?

AI

PHT↑↓ ↔

NCCP RFN⇓ STP⇓ TGB⇓ TPM⇓ VPA⇓ ↔

ZNS⇓

PB↑

AI

↔

PRM↓ RFN⇓ STP⇓ TGB⇓ TPM⇓ VPA⇓ ↔ PB↑

ZNS⇓

↔

↔

–

PRM↓ RFN↓ STP⇓ TGB⇓ TPM⇓ VPA⇓ PB↑

↔

↔

ZNS⇓

VPA↑ NA

↔

NA

NA

NA

NCCP PHT↑↓ NA

–

RFN⇓ STP⇓ TGB⇓ TPM⇓ VPA⇓ ↔

NA

? ?

NA ZNS⇓

PB↑

PHT↑

NA

?

–

?

?

↔

↔

NA

?

PB⇑

NA

NA

PRM⇑ ?

–

?

?

VPA⇑ NA

?

↔

↔

↔

?

?

–

NA

↔

NA

↔

↔

?

?

?

–

VPA↓ NA

PB⇑

PHT↑ ↔ PHT↓* ↔

PB⇑

RFN↑

↔

TPM↓ –

↔

PHT↓

NA

↔

RFN↓ NA

NA

NA

↔

PHT↑

NA

↔

?

NA

NA

?

abbreviations 

NA

ZNS

NA ?

↔

ZNS⇓

↔

–

NA

↔

NA

–

clobazam; DMCLB = N-desmethylclobazam (active metabolite of CLB); ESL = eslicarbazepine; OXC); LCM = lacosamide; LEV = levetiracetam; LTG = lamotrigine; OXC = oxcarbazepine; STP = stiropentol; TGB = tiagabine; TPM = topiramate; VPA = valproic acid; VGB = vigabatrin; ↓ = a usually minor (or inconsistent) decrease in plasma level; increase in plasma level; ⇑ = a usually clinically significant increase in plasma level.

309

Index

Index 310

Abinol 134 Absenor 274 Acetadiazol 1 Acetak 1 Acetar 204 acetazolamide 1–10 adverse effects 4–5 brand names 1 chemical name and structure 1 dosing and use 5–7 drug interaction profile 3–4 overall place in epilepsy treatment 9 pharmacokinetics 2–3 special populations 7–8 suggested reading/more information 9–10 therapeutics 1–2 Acortan 11 Actebral 19 Actebral Retard 19 ACTH (adrenocorticotropic ­hormone) 11–18 adverse effects 13–14 brand names 11 chemical name and structure 11 dosing and use 14–16 drug interaction profile 12–13 overall place in epilepsy treatment 16–17 pharmacokinetics 12 special populations16 suggested reading/more information 17–18 therapeutics 11–12 Acthar 11 Acthelea 11 Actinerval 19 Actinium 163 adrenocorticotropic hormone see ACTH Albox 1 Alepsal 181 Aleviatin 192 Aliseum 49 Alpentin 95

Amizepin 19 Amotril 40 Ancalixir 181 Andral 181 Anlin 49 Ansilor 134 Ansiolin 49 Antelepsin 40 Antenex 49 Antisacer 192 Anxira 134 Anzepam 134 Apaurin 49 Aphenylbarbit 181 Apilepsin 274 Aplacasse 134 Apo-Acetazolamide 1 Apo-Carbamazepine 19 Apo-diazepam 49 Apo-primidone 220 Apozepam 49 Apydan extent 163 Aripax 134 Asabium 31 Asamid 68 Assival 49 Ativan 134 Atrofen 181 Aurantin 192 Avigilen 204 Axonyl 204 Azepal 19 Azepan 49 Azol 1 Bamgetol 19 Banzel 230 Bapex 95 Barbilettae 181 Barbilixir 181 Barbiphenyl 181 Basitrol 19 Benzopin 49 Bialminal 181 Blugat 95 Bonatranquan 134

Braintop 204 breast feeding see specific drug, subentry special populations Brucarcer 19

Index

Calmpent 95 Calmpose 49 Camapine 19 Carazepin 19 Carba 19 Carbabeta 19 Carbadac 19 Carbagen SR 19 Carbalex 19 Carbamazepin-B 19 carbamazepine 19–30 adverse effects 22–4 brand names 19 chemical name and structure 19 dosing and use 24–6 drug interaction profile 21–2 overall place in epilepsy treatment 28–9 pharmacokinetics 20–1 special populations 27–8 suggested reading/more information 29–30 therapeutics 19–20 Carbapsy 19 Carbatol 19 Carbatol CR 19 Carbatrol 19 Carbazene 19 Carbazep 19 Carbazina 19 Carbinib 1 Carmapine 19 Carmaz 19 Carmian 19 Carmine 19 Carpin 19 Carzepin 19 Carzepine 19 Castilium 31 Celontin 145 Cercine 49 Cerebroforte 204 Cerebropan 204

Cerebrosteril 204 Cerebryl 204 Cerebyx 86 Ceregulart 49 Cerepar N 204 Cetam 204 Cetamid 1 Ceumid 124 children see specific drug, subentry special populations Ciclofalina 204 Cintilan 204 Clarmyl 31 Clerin 192 Cleveral 204 Clobamax 31 clobazam 31–9 adverse effects 34–5 brand names 31 chemical name and structure 31 dosing and use 35–6 drug interaction profile 33–4 overall place in epilepsy treatment 38–9 pharmacokinetics 32–3 special populations 36–7 suggested reading/more information 39 therapeutics 31–2 Clobazan 31 Clonapilep 40 Clonatryl 40 clonazepam 40–8 adverse effects 43 brand names 40 chemical name and structure 40 dosing and use 44–6 drug interaction profile 42–3 overall place in epilepsy treatment 47–8 pharmacokinetics 41–2 special populations 46–7 suggested reading/more information 48 therapeutics 40–1 Clonazepamum 40 Clonex 40 Clonopam 40

311

Clopax 31 Clostedal 19 Clozer 40 Comizial 181 Compaz 49 Condition 49 Control 134 Convulex 274 Coquan 40 Cortrosyn 11 Cumatil 192 Cuxabrain 204 Cyral 220

Index 312

D-Pam 49 Dalam 153 Dapakan 274 Degranol 19 Depacon 274 Depakene 274 Depakene-R 274 Depakin 274 Depakine 274 Depakine Chrono 274 Depakote 274 Depakote ER 274 Depakote Sprinkles 274 Depalept 274 Depalept Chrono 274 Depamag 274 Deprakine 274 Deprectal 163 Deproic 274 Desorate 274 Di-Hydan 192 Diacomit 238 Dialag 49 Diamox 1 Diamox Sequals 1 Diamox Sustets 1 Diano 49 Diapam 49 Diapin 49 Diapine 49 Diapo 49 Diastat 49 Diaz 49

Diazem 49 Diazemuls 49 diazepam 49–58 adverse effects 52–3 brand names 49 chemical name and structure 49 dosing and use 53–5 drug interaction profile 52 overall place in epilepsy treatment 57 pharmacokinetics 50–1 special populations 55–7 suggested reading/more information 57–8 therapeutics 49–50 Diazepam Desitin 49 Diazepam-Eurogenerics 49 Diazepam-Lipuro 49 Diazepam-ratiopharm 49 Diazepam RecTubes 49 Diazepan 49 Diazer 49 Diazerekt 49 Difetoin 192 Dilantin 192 Diluran 1 Dinagen 204 Dineurin 95 Dintoina 192 Dipaz 49 Dipezona 49 Diphantoine 192 Diphantoine Z 192 Diphedan 192 Diproex ER 274 Dipromal 274 Ditoin 192 Ditomed 192 Diural 1 Diuramid 1 Divalproex 274 Docpirace 204 Doricum 153 Dormicum 153 Dormital 181 Dormonid 153 Doval 49 Ducene 49

Dupin 49 DZP 49

Felantin 192 felbamate 77–85 adverse effects 80–1 brand names 77 chemical name and structure 77 dosing and use 81–2 drug interaction profile 79 overall place in epilepsy treatment 84 pharmacokinetics 78–9 special populations 83–4 suggested reading/more information 85 therapeutics 77–8 Felbamyl 77 Felbatol 77 Fenatoin 192 Fenemal 181 Fenidantoin S 192 Fenitoina 192 Fenitoina Rubio 192

Index

Edhanol 181 Elcion CR 49 elderly people see specific drug, ­subentry special populations Elmendos 111 Elpenor 19 Emeside 68 Emoten 134 Emotival 134 Encefalux 204 Encetrop 204 Engaba 95 Epamin 192 Epanutin 192 Epazin 19 Epikor 19 Epilan-D 192 Epilantin 192 Epileptin 192 Epileptol 19 Epileptol CR 19 Epilex 274 Epilim 274 Epilim Chrono 274 Epilim Chronosphere 274 Epilramate 263 Epinat 192 Episenta 274 Epitomax 263 Epitop 263 Epival 274 Epiven 95 Epleptin 95 Eposal Retard 19 Eptoin 192 Ergenyl 274 eslicarbazepine acetate 59–67 adverse effects 61–2 brand names 59 chemical name and structure 59 dosing and use 62–4 drug interaction profile 61 overall place in epilepsy treatment 66 pharmacokinetics 60–1

special populations 64–6 suggested reading/more information 66–7 therapeutics 59–60 Espa-lepsin 19 ethosuximide 68–76 adverse effects 70–1 brand names 68 chemical name and structure 68 dosing and use 71–3 drug interaction profile 70 overall place in epilepsy treatment 75 pharmacokinetics 69–70 special populations 73–4 suggested reading/more information 75–6 therapeutics 68–9 Ethymal 68 Etomal 68 Etosuximida 68 Euphorin 49 Evamox 1 Everiden 274 Exalief 59 Excegran 297

313

Index 314

Fenitoina Sodica 192 Fenitron 192 Fenobarbital 181 Fenobarbitale 181 Fenobarbitale Sodico 181 Fenton 181 Fenytoin 192 Finlepsin 19 Flavis 204 Fluozoid 68 Fomiken 192 Fonurit 1 Fortanest 153 Fosolin 86 fosphenytoin 86–94 adverse effects 89 brand names 86 chemical name and structure 86 dosing and use 89–92 drug interaction profile 88 overall place in epilepsy treatment 93–4 pharmacokinetics 87–8 special populations 92–3 suggested reading/more information 94 therapeutics 86–7 Frisium 31 Fulsed 153 Gabacet 204 Gabadin 95 Gabahexal 95 Gabalep 95 Gabantin 95 Gabapenin 95 gabapentin 95–103 adverse effects 98 brand names 95 chemical name and structure 95 dosing and use 98–100 drug interaction profile 97 overall place in epilepsy treatment 102–3 pharmacokinetics 96–7 special populations 101–2 suggested reading/more information 103 therapeutics 95–6 Gabatin 95

Gabatine 95 Gabatopa 263 Gabax 95 Gabexol 95 Gabietal 95 Gabitril 255 Gabix 95 Ganin 95 Gantin 95 Gapalept 95 Gapatin 95 Gapridol 95 Gardenal 181 Gardenal Sodium 181 Gardenale 181 Gaty 95 Genogris 204 Geram 204 Geratam 204 Gericarb SR 19 Gewacalm 49 Glaupax 1 Gratusminal 181 Grifoclobam 31 hepatic impairment see specific drug, subentry special populations Hermolepsin 19 Hidanil 192 Hidantoina 192 Horizon 49 Huberdasen 204 Huma-Zolamide 1 Hydantin 192 Hydantol 192 Hypnovel 153 Ifa Fonal 49 Ikaphen 192 Iktorivil 40 Inovelon 230 Ipnovel 153 Kalicor 204 Kaptin 95 Karbamazepin 19 Karidium 31 Kenoket 40 Keppra 124 Keppra XR 124

Klonopin 40 Kopodex 124 Kratium 2, 49 Kratium 49 Kriadex 40 Kutoin 192

Index

Labicitin 111 Labileno 111 lacosamide 104–10 adverse effects 106–7 brand names 104 chemical name and structure 104 dosing and use 107–8 drug interaction profile 105–6 overall place in epilepsy treatment 110 pharmacokinetics 105 special populations 108–9 suggested reading/more information 110 therapeutics 104–5 Lamdra 111 Lamepil 111 Lamictal 111 Lamictin 111 Lamidus 111 Lamitor 111 Lamitrin 111 Lamodex 111 Lamogin 111 Lamogine 111 lamotrigine 111–23 adverse effects 114–16 brand names 111 chemical name and structure 111 dosing and use 116–19 drug interaction profile 113–14 overall place in epilepsy treatment 121–2 pharmacokinetics 112–13 special populations 119–21 suggested reading/more information 122–3 therapeutics 111–12 Lamotrix 111 Lamozine 111 Lansden 40

Lantidin 192 Larpose 134 Latrigine 111 Laubeel 134 Lauracalm 134 Ledamox 1 Lediamox 1 Lehydan 192 Lembrol 49 Lepinal natrium 181 Leptilan 274 Leptisol 19 Lethyl 181 levetiracetam 124–33 adverse effects 127–8 brand names 124 chemical name and structure 124 dosing and use 128–30 drug interaction profile 126–7 overall place in epilepsy treatment 131–2 pharmacokinetics 126 special populations 130–1 suggested reading/more information 132–3 therapeutics 124–6 Liskantin 220 Logem 111 Logical 274 Logical Jarabe 274 Lonazep 40 Lonazet 163 Lonza 134 Lopam 134 Lora 134 Lorabenz 134 Lorafen 134 Loram 134 Lorans 134 Lorapam 134 Lorax 134 Loraxepam-Efeka 134 Lorazene 134 Lorazep 134 lorazepam 134–44 adverse effects 138–9 brand names 134 chemical name and structure 134

315

Index 316

lorazepam (Cont.) dosing and use 139–41 drug interaction profile 137 overall place in epilepsy treatment 142–3 pharmacokinetics 136–7 special populations 141–2 suggested reading/more information 143–4 therapeutics 134–6 Lorazepam-Eurogenerics 134 Lorazin 134 Lorazon 134 Lorenin 134 Loridem 134 Lorivan 134 Lorsilan 134 Lorzem 134 Lotrigine 111 Lucetam 204 Lucium 31 Lumcalcio 181 Luminal 181 Luminale 181 Luminaletas 181 Luminalette 181 Luminaletten 181 Luminalum 181 Lyrica 212 Lytenur 204 magnesium valproate 274 Majsolin 220 Medene 1 Melode 49 Menobarb 181 Merapiran 204 Merlit 134 Merlopam 134 methsuximide 145–52 adverse effects 147–8 brand names 145 chemical name and structure 145 dosing and use 148–9 drug interaction profile 146–7 overall place in epilepsy treatment 151

pharmacokinetics 146 special populations 150–1 suggested reading/more information 151–2 therapeutics 145–6 Midacum 153 Midanium 153 Midazo 153 Midazol 153 midazolam 153–62 adverse effects 156–7 brand names 153 chemical name and structure 153 dosing and use157–9 drug interaction profile 155–6 overall place in epilepsy treatment 160–1 pharmacokinetics 154–5 special populations 159–60 suggested reading/more information 161–2 therapeutics 153–4 Midazolam Torrex 153 Midolam 153 Midozor 153 Miloz 153 Mizodin 220 Mizolam 153 Mogine 111 Movileps 192 Mutigan 220 Myidone 220 Mylepsinum 220 Myocalm 204 Mysoline 220 Neosidantoina 192 Nepatic 95 Nervistop L 134 Neugeron 19 Neuril 95 Neurium 111 Neurobiol 181 Neurolep 19 Neuronova 204 Neurontin 95 Neuropam 134

Oikamid 204 Optamide 1 Orfidal 134 Orfiril 274 Orfiril Retard 274 Ortopsique (MX) 49 Ospolot 246 oxcarbazepine 163–72 adverse effects 166–7 brand names 163 chemical name and structure 163 dosing and use 167–9 drug interaction profile 165–6 overall place in epilepsy treatment 171–2 pharmacokinetics 164–5 special populations 169–71 suggested reading/more information 172 therapeutics 163–4

Oxetol 163 Oxrate 163 Paceum 49 Pacitran 49 Panitol 19 Paral 173 paraldehyde 173–80 adverse effects 175–6 brand name 173 chemical name and structure 173 dosing and use 176–8 drug interaction profile 174–5 overall place in epilepsy treatment 179 pharmacokinetics 174 special populations 178 suggested reading/more information 179–80 therapeutics 173 Pax 49 Paxam 40 Paxum 49 Pendine 95 Pengatine 95 Pepsytoin-100 192 Petilin 274 Petimid 68 Petinimid 68 Petinutin 145 Petnidan 68 Pevalon 181 Phenaemal 181 Phenhydan 192 Phenilep 192 phenobarbital 181–91 adverse effects 184–5 brand names 181 chemical name and structure 181 dosing and use 185–8 drug interaction profile 183–4 overall place in epilepsy treatment 189–90 pharmacokinetics 182–3

Index

Neurotol 19 Neurotop 19 Neurotop Retard 19 Neurtrol 163 Neuryl 40 New-GABA 95 Nivalen 49 Nixtensyn 49 Noan 49 Noiafren 31 Noodis 204 Noostan 204 Nootron 204 Nootrop 204 Nootropicon 204 Nootropil 204 Nootropyl 204 Nopatic 95 Normabel 49 Normabrain 204 Norzetam 204 Novhepar 134 Novocephal 204 Nu-Loraz 134 Nupentin 95

317

Index 318

phenobarbital (Cont.) special populations 188–9 suggested reading/more information 190–1 therapeutics 181–2 Phenobarbiton 181 Phenobarbitone 181 Phenobarbiton-natrium 181 Phenotal 181 phenytoin 192–203 adverse effects 196–7 brand names 192 chemical name and structure 192 dosing and use 197–200 drug interaction profile 194–6 overall place in epilepsy treatment 201–2 pharmacokinetics 193–4 special populations 200–1 suggested reading/more information 202–3 therapeutics 192–3 Phenytoin KP 192 Phenytoinum 192 Pirabene 204 Piracebral 204 Piracemed 204 piracetam 204–11 adverse effects 207 brand names 204 chemical name and structure 204 dosing and use 207–9 drug interaction profile 206–7 overall place in epilepsy treatment 210–11 pharmacokinetics 205–6 special populations 209–10 suggested reading/more information 211 therapeutics 204–5 Piracetam AbZ 204 Piracetam AL 204 Piracetam EG 204 Piracetam Elbe-Med 204 Piracetam-Farmatrading 204 Piracetam Faro 204 Piracetam Heumann 204

Piracetam Interpharm 204 Piracetam-neuraxpharm 204 Piracetam Prodes 204 Piracetam-R Ph 204 Piracetam-ratiopharm 204 Piracetam Stada 204 Piracetam Verla 204 Piracetam von ct 204 Piracetop 204 Piracetrop 204 Pirax 204 Pirazetam-Eurogenerics 204 Placidox 49 Plexxo 111 Plidan 49 Povanil 40 Pragmaten 274 pregabalin 212–19 adverse effects 214–15 brand name 212 chemical name and structure 212 dosing and use 215–17 drug interaction profile 214 overall place in epilepsy treatment 218–19 pharmacokinetics 213 special populations 217–18 suggested reading/more information 219 therapeutics 212–13 pregnancy see specific drug, subentry special populations Primidon 220 primidone 220–9 adverse effects 223–4 brand names 220 chemical name and structure 220 dosing and use 224–6 drug interaction profile 222–3 overall place in epilepsy treatment 228 pharmacokinetics 221–2 special populations 227–8 suggested reading/more information 229 therapeutics 220–1

Pro-Epanutin 86 Prodilantin 86 Prolepsi 163 Propam 49 Protalgine 111 Prysoline 220 Psicopax 134 Psychopax 49 Psycoton 204 Pyoredol 192 Pyramen 204 Qropi 204

Sabril 288 Sabrilan 288 Sabrilex 288

Index

Radizepam 49 Ravotril 40 Rectubes 49 Reinin 95 Relacum 153 Relanium 49 Relsed 49 renal impairment see specific drug, subentry special populations Renamid 1 Renaquil 134 Renborin 49 Riklona 40 Rivatril 40 Rivotril 40 Ronton 68 rufinamide 230–7 adverse effects 232–3 brand names 230 chemical name and structure 230 dosing and use 233–4 drug interaction profile 232 overall place in epilepsy treatment 236 pharmacokinetics 231 special populations 235–6 suggested reading/more information 236–7 therapeutics 230–1

Seaze 111 Sedacum 153 Sedatival 134 Sederlona 31 Seduxen 49 Sepibest 19 Serenzin 49 Sertan 220 Sevenal 181 Sidenar 134 Silence 134 Sinapsan 204 Sinergina 192 Sipam 49 Sirtal 19 sodium divalproate 274 sodium valproate 274 Solfoton 181 Sopodorm 153 Stapam 134 Stazepine 19 Stazol 1 Stedesa 59 Stesolid 49 Stesolid Rectal Tube 49 Stimubral 204 stiripentol 238–45 adverse effects 240–1 brand name 238 chemical name and structure 238 dosing and use 241–3 drug interaction profile 240 overall place in epilepsy treatment 244–5 pharmacokinetics 239 special populations 243–4 suggested reading/more information 245 therapeutics 238–9 sulthiame 246–54 adverse effects 248–9 brand name 246 chemical name and structure 246 dosing and use 249–51 drug interaction profile 248 overall place in epilepsy treatment 252–3

319

sulthiame (Cont.) pharmacokinetics 247 special populations 251–2 suggested reading/more information 253–4 therapeutics 246–7 Sunzepam 49 Suxilep 68 Suximal 68 Suxinutin 68 Synacthen 11 Synaptine 204 Synomax 1

Index 320

Taloxa 77 Taver 19 Tavor 134 Tegol 19 Tegral 19 Tegretal 19 Tegretol 19 Tegretol CR 19 Tegretol Retard 19 Temesta 134 Temporol 19 Teril-CR 19 tiagabine 255–62 adverse effects 257–8 brand name 255 chemical name and structure 255 dosing and use 258–60 drug interaction profile 257 overall place in epilepsy treatment 261–2 pharmacokinetics 256 special populations 260–1 suggested reading/more information 262 therapeutics 255–6 Timonil 19 Timonil Retard 19 Timox 163 Titus 134 Topamac 263 Topamax 263 Topamax Sprinkle 263 Topepil 111 Topimax 263

Topinmate 263 topiramate 263–73 adverse effects 266–7 brand names 263 chemical name and structure 263 dosing and use 268–70 drug interaction profile 265–6 overall place in epilepsy treatment 271–2 pharmacokinetics 264–5 special populations 270–1 suggested reading/more information 272–3 therapeutics 263–4 Topirid 263 Topitrim 263 Topomac 263 Tranqipam 134 Tranquirit 49 Trapax 134 Trapex 134 Trepina 19 Trexapin 163 Tridezibarbitur 181 Trileptal 163 Trileptin 163 Trofocortina 11 Uni-Feno 181 Uramox 1 Urbadan 31 Urbanil 31 Urbanol 31 Urbanyl 31 Utoin 192 Uzolam 153 Valaxona 49 Valcote 274 Valdimex 49 Valiquid 49 Valisanbe 49 Valium 49 Valiuzam 49 Valpakine 274 Valpam 49 Valparin 274 Valporal 274

suggested reading/more information 296 therapeutics 288–9 Vigiten 134 Vimpat 104 Volclair 49 Vulsivan 19 Vultin 95 Vupral 274 Zarondan 68 Zarontin 68 Zebinix 59 Zepanc 40 Zeptol CR 19 Zolmide 1 Zonegran 297 zonisamide 297–306 adverse effects 300–1 brand names 297 chemical name and structure 297 dosing and use 301–3 drug interaction profile 299 overall place in epilepsy treatment 305–6 pharmacokinetics 298–9 special populations 303–5 suggested reading/more information 306 therapeutics 297–8 Zora 134 Zymanta 40

Index

Valprax 274 Valpro 274 valproate 274–87 adverse effects 278–80 brand names 274 chemical name and structure 274 dosing and use 280–3 drug interaction profile 277–8 overall place in epilepsy treatment 285–6 pharmacokinetics 275–7 special populations 283–5 suggested reading/more information 286–7 therapeutics 274–5 valproic acid 274 Vanconin 49 Vatran 49 Vematina 274 Versed 153 vigabatrin 288–96 adverse effects 290–1 brand names 288 chemical name and structure 288 dosing and use 291–4 drug interaction profile 289–90 overall place in epilepsy treatment 295–6 pharmacokinetics 289 special populations 294–5

321